Texas: Being Sued For A Deceased Relative's Unpaid Property Taxes?

This is a slightly complicated story but I'll do my best to not go on a tangent. My(26) grandma, who passed in 2021, had a plot of land in a county we no longer live in. She then made a deal with a couple over 25 years ago, when she still lived there, where they would make payments to her and eventually she would give them the land (payments were for the sale). This agreement included the couple pay the property taxes because the payments my grandma had them make were very small. I'm not sure when they finished making their payments, but around 2018 my dad (who passed in 2023) went to meet with the couple because my grandma was notified of overdue property taxes. From my understanding, and from a bunch of "he said/she said", my dad and the male got into a heated argument. The male wanted my grandma/dad to transfer the title for the land, and my dad explained to him he couldn't transfer the title until the taxes were paid off. The man then told my dad he wouldn't pay the taxes until the title was in his name (which wasn't possible with the unpaid taxes)... No one else in my family knew anything about this land. Just my dad and my grandma. We can not find any paperwork regarding the legitimacy of this deal because unfortunately all my other family members, who were adults at that time, did not think it was important to get involved.

My younger brother (25) got a call from a lawyer on Wednesday. The lawyer was looking for my dad because the county is suing my grandma for about 8 years of owed property taxes, and my brother has the same name as my dad. My brother informed the lawyer of my grandma and dad's passing. The lawyer then informed my brother that him, myself, and my little sister (17) are all liable for the taxes as we are considered heirs. My grandma also had two other kids aside from my dad - both who are still living. The lawyer told us all five of us would have to sign a form stating we are not interested in the land because my grandma did not leave a will (as far as I know). The lawyer also told my brother that the owed property taxes are only about 7k, which we do collectively have. So we can potentially pay the taxes off and transfer the land, then possibly sell it for more. The issue is the couple is actively living on the property, in a home they built on it. After some internet searching I was able to find the names of the couple (which none of my living older relatives knew...), and my aunt (grandma's daughter) contacted them. She told them the situation and they told us they are supposedly meeting with a lawyer to work out a payment arrangement.

My aunt does not see this as our problem. She sees it as the couples problem and she isn't concerned with the lawsuit effecting me or my siblings. If they don't pay off the taxes, she thinks we should pay them off and then sell the land. I think it will be much more of a hassle, with many potential legal issues especially if the couple has proof of the agreement and payments. I think our best course of action is to sign the paperwork the lawyer suggested so we are no longer liable. But I am hoping to get some advice on this situation.

There is an issue with taking the route of giving up the rights to the land. My grandma's third child, my uncle, who is an alcoholic that we all decided to no longer engage with after he physically and mentally abused my grandma in her final days. Based on the lawyers words, he will need to also sign away his rights to the land. This man is very money hungry, and I do not think he will do that. If this is the route we take, will we still be liable if he doesn't sign his rights away? Or just him?

I'm in my final semester of graduate school, so money is very tight right now. But if I need to consult a lawyer I will because I don't want any of my siblings or myself to be burdened by the mistakes my dad and grandma made.