What are the rights of a sister in law in a property after being sold?

There are a lot of different angles to your question. Basically, it seems to me that living in property and paying only the property tax might be a pretty good deal depends on the property. You don't say who these women are married to heirs / owners of the property? (A person has heirs; property has owners). Anyway, a lot more details are needed to give a cogent answer, but here's a practical thought how much money are we talking about? Have they lived there 10 years, so that they're looking for $50,000 in property tax? Or a year, so they're looking for maybe a 10th of that? Also, have they moved out? Or are the owners going to need to evict them to get them out? If they are still in the property, and each is looking for a couple of thousand dollars, then make a "cash for keys" deal they move out and take all their stuff with them, and the owners will pay the property tax.

If there was an agreement to pay property taxes in lieu of rent then they should pay the property taxes incurred while they resided on the property.

Not enough information is provided. It is not clear how you are interested in this, at all. Your spouse could potentially have a claim, but you would not be an heir, so it is not clear how you would be able to act, at all. It is also generally not necessary for an heir to pay rent. ALL heirs would have been entitled to possess the property, as co-owners. Since they paid to maintain the property that you all owned, arguably, they should be entitled to reimbursement from the proceeds.

The sister-in-laws have no rights to the proceeds, only the heirs. If someone has not paid on the property tax, this amount can be taken from the individual who did not pay, before they receive their share.