Second, you should have an accountant advising you.
Based on what you've stated, you'd be owed $51,000. That's the $1,000 per month for 51 months.
However, your question is unclear. Did the family agree to share in the appreciation? If so, what did that part of the agreement say?
If there was some sort of shared equity agreement, it would probably begin when you became involved, in 2005. So the question would be: What was the house worth in 2005?
Let's make some numbers up. Let's say it was worth $300,000 in 2005. (A Realtor can help you determine what it really was worth. And let's say your agreement was that your equity would be the $1,000 a month plus 50% of the appreciation. There are a number of different ways to calculate it, but here's one: When the property was sold, it sold for $470,000. Your $1,000 a month came to $51,000. You get that back, off the top.
Total appreciation was $170,000 ($470,000 sales price minus the $300,000 it was worth when you became involved in 2005). If you're entitled to half, you're entitled to $85,000 worth of appreciation. So, the total amount due you would be $136,000 ($51,000 plus $85,000).
Obviously, the critical issue is how much appreciation you were entitled to. It's also important to know what the house was worth in 2005 if you're entitled to any appreciation from that point.
Hope that helps.
It would seem likely that you will have a battle on your hands.
You should assemble a TEAM with at least a CPA and an Attorney.
Realtors will not advise you on TAX nor LEGAL matters.
Good luck and may God bless
There are as many ways to calculate this as there are people who may calculate it. There are also many missing parts to consider. Is there a lien against the property? Did you do any improvements or damage? What is the assessed value today versus then? Assessments only very roughly relate to market value.
I believe you are going to have to create a proposal to present to the other owners and see if they accept, reject or modify it. You could also decide as a group to hire someone familiar with real estate, mortgage and accounting to come up with a number that all would agree to accept.