Yes RI does recognize MA letters. You will have to go through a process called ancillary probate to obtain letters in RI to allow you to address...

Who is he? .............................................

Sue who? Your father? Probably. ..................................

When a person pays taxes, even when not the owner, this does not change the ownership of the house.

Sounds like you need to go see and retain an attorney.

Father-in-law's heirs inherit father in laws share unless the deed specifically indicated that the survivor receives the entire property.

Fire your unresponsive attorney and ask for your money back. Retain a new attorney.

Does the non-motorized travel trailer have a formal title? Can you get it updated without going to the probate court? If not, you need an order...

A deed is effective when executed. If a deed is recorded, then third parties have constructive notice of the deed.

No legal duty exists to clean up dead brother's "junk."