Can I sue for mental anquish against my uncle estate of his step-graddaughter inherits any of his land?

I hope you see this answer, because it isn't possible to e-mail you as you requested. Attorneys who see questions posted in this forum aren't given e-mail addresses for the posters. I am sorry to hear that your uncle is such an unpleasant person, and I am very sorry that your aunt has gotten herself involved in a situation where she owns real estate with him. This is a very good example of the type of situation which unfortunately often results when family members purchase real estate together, and is the reason I tell most of my clients NOT to buy real estate with siblings or other non-spouse relatives. If your uncle owns an interest in the real estate, he owns an interest in the real estate. Your aunt might be able to sue to have the property partitioned, and she might have some ability to try to sue him for his share of taxes and other expenses, but those are not actions that would normally be steps you could take unless you were your aunt's legally appointed conservator or the legally appointed executor or administrator of her estate. Your uncle's interest in the property is his, and he is free to leave it to his wife if he wants to do so. You can't sue him or anyone else just because you don't like that idea. I am sure you mean well and would like to help your aunt, but quite honestly if she is willing to let her brother treat her so badly there isn't really anything you can do about that. If the situation distresses you, then your only option may be to remove yourself from it by moving out of your aunt's house (without regard for where she ends up if you do) and letting go of any idea that this property can be kept away from your uncle and his wife.