How to buy out a third of a property share

[MrsDinero]

Semi-hypothetical question.

Our uncle (in his 60's) is currently living in a home that was passed to him and his two sisters on the passing of their father in early 2000.

His living in the house was on the condition of taking care of it.  Now that one sister (my MIL) has passed the other sister has been slowly applying pressure to her brother to sell this house.  If they end up selling the house, it is doubtful he would be able to find a better deal because this house has no mortgage.  He also paysthe property taxes. 

The current ownership of the house is, our uncle, our aunt, and my FIL.

My husband and I are considering offering to buy out the aunt for her portion of the house.  We would like to see our uncle stay in that house as long as he wants to, so this would not be considered an investment property.  How would we go about doing this?  The housing market in that area isn't that great.  The current Zestimate (I know not accurate) is $155k.

[Another Reader]

Call  her up, tell her you would like to buy her third out, and get an appraisal.  If all parties agree on the appraised value, write the check.

If you don't do this, the aunt could force a partition, which would mean a court-ordered sale.

ETA:  If he has a "life estate" in the property, which he may have, given he is required to pay the property taxes, the property is encumbered and the value of the aunt's interest is less than a third of fair market value.   She would not be able to get full value even if she could force a partition in that situation.