I am an owner of a property of an undivided interest with my two other sisters.

There are two issues here: what your uncle promised when you signed the partition deed, and what you can do about the house you now own with your sisters.

First, have an attorney review the signed partition deed, the amendment, and any texts or other writings about the $60,000 payment. Whether your uncle owes you that money depends on what those documents say and what you agreed to. His statement that you must accept $20,000 less does not, by itself, establish that you agreed to a reduction.

As for the house, if you and your sisters each own an undivided interest, you can seek a partition even if one sister refuses to cooperate. You cannot force her personally to buy your share, but a partition case may give her an opportunity to do so. If the house cannot fairly be divided, the court can order a sale and divide the proceeds according to the owners’ interests, with any appropriate adjustments. Because the property came through your family, special rules for heirs’ property may apply.

Your sister’s living in the house does not automatically mean she owes you rent. Her refusal to let you enter or use it may support a claim for your share of its reasonable rental value, depending on the evidence of when and how she excluded you. If her adult children pay her rent, you may also be entitled to an accounting of your share of the rent she received. Their living there alone does not establish that rent is owed.

Take the deed, amendment, payment communications, and any messages denying you access to a Texas attorney who handles property disputes in the county where the house is located. The attorney can assess the $60,000 claim and whether to pursue partition and an accounting for your sister’s use of the property.