The sellers (3 siblings) have requested a letter of intent to purchase and are working with a lawyer as this house was in probate for 3 years.

I just feel that it'll be disrespectful selling a gift immediately after it was given to you by a sibling.  

I tried to get everyone to sign a new lease (same price), but it got complicated...the OTHER (younger and healthier daughter who doesn't live there) said that the siblings that live with her mom don't have any income, hence why they won't sign the new lease.

We just probated my MIL's estate and had to lay out attorney fees, and the process took about a year with everything working OK, no squabbling siblings, no other heirs coming out of the woodwork.

I am wonder if there is any advice on what course of action my siblings and i should take.

It was left to me & my siblings by our mother who passed in 2013.

Direct defendants = 4.5%, siblings = 12%, and others = 15%.  

This stubborn old man is 67 and believes that he is still owned something from his siblings and is making very difficult for my entire family.

You know, I come from a huge family 10 siblings on each of my parents sides being a Native American.

There are 2 other out of state siblings that may have a claim.