Thank you for the information and your question. Although Massachusetts does recognize "adverse possession," (which is the legal term for squatter's rights, there are certain minimum requirements that must be fulfilled in order to qualify. Unfortunately, it does not appear that you can satisfy all of them because one of them is that you on are the property without the owner's consent. Since you did have consent from your husband's father, it would not be adverse. You can see the requirements below.
1) You were the exclusive possessor and actually entered the property.
2) Your possession was "open and notorious." Meaning that people could see you had possession of the land. The possession was appropriate for the type, size and use of the land. Enclosures, houses, cabins, payment of taxes all help establish your claim. The general idea is to give the "actual" owner reasonable notice that you were in possession and give him the opportunity to eject you.
3) Your possession must be adverse to the owners claim, in other words without the owners consent. If the owner gave permission for you to be on the property you can't claim the property adversely.
4) Your possession must be continuous for 20 years. But, certain seasonal or intermittent uses satisfy the continuous element if the average owner of a particular piece of property would use it in that same way (like a summer home or hunting lodge).
The only other type of right to continued possession of land is usually by way of easements
. If you could establish that the permission you received was a permanent easement, then you might be successful in the continued use of the property. However, it would not be easy or inexpensive to do since you would need to hire a real estate
attorney to file suit to have the easement established as a property right.
Please let me know if you need any clarification. I would be glad to assist you further if I can.