I see that the question has drifted from "Can my husband and i use the same altar?" to "Should i set up an ancestor altar to venerate my parents, who were not together in life and who also had alcohol and drug addictions?"
So, i will leave the question of your husband and altar-sharing behind, and move on to the question of what constitutes a worthy ancestor and how those of us who have what some might call "wounded" ancestors can handle their conflicted emotions of love, gratitude, affection, despair, anger, and hatred and forge a bond with ancestors who were troubled and troubling while alive.
For this reason, i have moved your new question, FiachnaCybele's reply to it, and this reply of mine to a new topic thread -- "Graveyard, Ancestors, Mediumship, Dying, Death, The Dead."
As FiachnaCybele said, any decisions you make will have to be personal, but i would like to add that because you are not the first person who has walked this path, there happens to be quite a lot of religious theory and community wisdom on the subject, and it is available to you, should you choose to take it.
This material is adapted from an old Lucky Mojo Shop Flyer that i wrote, and which we used to print and give out to customers.
Ancestor veneration, Spiritism, and Spiritualism, as practiced in the Americas since the 1850s , are what we call "open congregation" religions. That is, you do not have to be born as the descendant of someone in the religion, nor do you need to be initiated in order to participate in the practice of the religion, nor is your entrance into the religion mediated by a member of the clergy (such as a priest or priestess) who can gainsay your admission, nor do you need to undergo any sort of ordeal trial or probationary period before being allowed to perform venerations according to the precepts of the religion.
Because of their loose structure in modern times, open congregation religions do have a tendency toward loose community bonds, and some are engaged by solitary practitioners, outside a physical church structure. When practiced in the home, they are also part of what are called "domestic religions."
The fact that some religions have an open congregation structure and are practiced in the home does NOT mean that they have no body of shared community wisdom and practice. It does NOT mean that they are something you can "make up as you go along."
Also be aware that not all open congregation religions are domestic religions and not all domestic religions are open congregation religions. Nor are either restricted to religions that include ancestor veneration. They overlap, and i am discussing the religious practices that fall within the area of overlap between open congregation and domestic religions -- and also overlap with the set of religions which include the practice of ancestor veneration.
In order to engage in the practices of a domestic and / or open congregation ancestor veneration religion, you would do well to meet others who are also members of the religion and learn from them the continuity and customs of the practice. Failing that, you ought to read books, watch videos, and otherwise receive and put into practice the historical wisdom and knowledge of the religion.
As an example, the domestic ancestor veneration of the ancient Romans differs from that of the modern Kardecian Spritists, and both differ from the practices of the modern Spiritual Church Movement. Each has many interesting qualities, and, believe me, each has grappled with the issue of "unworthy ancestors." How this matter is resolved within each religion is a matter of local culture and custom. There is no one answer to the question. Either you can do as FiachnaCybele suggested, and pioneer your own way through the problem, or you can take my advice, offered freely, which has gained many adherents, and is certainly well known and well practiced at this time.
But first, let us look at our options. There are, essentially, five -ways to deal with unwanted ancestor spirits -- and each has been the custom in one culture or another, at different times:
1) Entrapment. Spirits can be trapped in containers. This method is commonly used to collect and dispose of demons or djinns. It may also be undertaken with ghosts and ancestral spirits. The key to its effectiveness is the proper disposal of the spirit trap. It may be sunk in the sea, taken out to the desert, or buried in a cemetery, as appropriate.
2) Banishment. The unworthy ancestors can be exiled or banished from the altar. They are divorced from the family. In many cultures, this is accomplished by visiting the grave, presenting a list of grievances, and spitting or pissing on the grave of the ancestor, with a final curse.
3) Release. The unworthy ancestors can be forgiven and released to go on to meet their God, or be reborn, or go to Hell, or go to Heaven, according to whatever afterlife cosmology one accepts. This is often done by calling upon higher spirits such as angels, archangels, or god(s) to administer to the ancestor whatever punishment or reward is to be meted out. This can be accomplished by scattering flowers on their graves or dispersing their ashes into the wind or the sea.
4) Negotiated or Mediated Contact. The unworthy ancestors may be contacted in spirit by a professional trance medium, who will convey and relay messages to them and from them. This may develop into a protracted series of mediumistic seances within a Spiritualist church or consulting room setting, but it is also possible to uncover a mediumship gift within oneself and to make the contacts in the home. Negotiated contact is, alas, subject to fraud on the part of false mediums, so it must be entered into with absolute trust and confidence. In particular, be wary of any spirit medium or ancestor reader who tells you that you must pay for expensive gifts or an elaborate ceremony in order to "settle" the ancestors, and that they will "haunt" you if you fail to pay.
5) Elevation. The unworthy ancestors can be asked to mend their unfortunate ways and can be guided in an upward and redemptive path through which, as spirits, they will come to see what they did wrong, to cast aside their frailties, and to become worthy members of the spirit world. This is accomplished with an actual physical piece of domestic altar work, called an ancestor elevation. There are many versions of such a ceremony, but an especially traditional one can be found in the book "Deliverance" by Khi Armand.
Study and learn, for in the end is YOU, not a priest or a root doctor, who must choose which course your acknowledgement and veneration of these troubled ancestors will take. Here is a link to the book "Deliverance" --
BOO-GRI-DELI
Deliverance by Khi Armand
$12.00
You can order right here in the Forum by clicking on the blue Add To Cart button.
Contents
Dedication 4
Acknowledgements 4
About This Book 5
Who Will Deliver Us? 6
What Is Hoodoo? 7
The Terminology of Conjure 8
On the Purchase of Spiritual Products 9
On Botanicals, Minerals, and Animal Curios 10
Diagnosing Spiritual Problems 11
Understanding Magic 11
Understanding Spiritual Gifts 13
Understanding Initiatory Crises 14
Understanding Jinxes and Crossed Conditions 16
Understanding Intrusive Spirits and Energies 17
Understanding Curses 18
Interpreting Dreams, Signs, and Omens 20
Formal Methods of Divination and Reading 23
Spiritual First Aid Spells 26
Uncrossing and Spiritual Cleansing 29
Uncrossing Money: Deliverance from Poverty 39
Uncrossing Love: Deliverance from Loneliness 45
Uncrossing Health Matters 49
Uncrossing Legal Matters 54
Dealing with Intrusive Spirits and Energies 58
Reversing and Protection 60
Carrying the Good Work On 66
Unlocking Clarity and Self-Mastery 66
When You Are Stuck: Block Buster Work 69
When You Are Ready: Road Opener Work 71
Maintenance: How Often Should You Cleanse? 72
Developing Relationships with Helping Spirits 73
Developing Relationships with Ancestors 74
Developing Relationships with Angels and Saints 79
How to Find the Right Root Doctor 86
Spiritual and Social Resources 89
Frequently Asked Questions 90
Bibliography 96
spirit traps are something i haven't done much work with, but i have heard the Martin Coleman book (do you know if it's true it was really Draja Mickaharic who wrote it?), guess it's time i finally picked it up. 
