Unknown or unfounded Heirs

[Cheyenne Hamilton]

Need a little help. My mother-in-law is wanting to sell a property that she is 30% heir in. 

Another heir who is entitled to 40% of the property ownership is also in agreement to sell. 

There was another known heir the passed with no children to pass her ownership to and a few others that can’t be located. 

Any advice for getting the property sold? A few local small town lawyers have been very unhelpful. Was thinking maybe selling and setting the remaining 30% in a trust for remaining heirs in case they popped up down the road but unsure.