My Husband Inherited 1/3 Of 77 Acres When His Dad Died. His Dad's Girlfriend, Who Owns The Other 2/3, Is Charging Us Rent To Live In The Second House. She Also Wants To Sell The Tractor That He Owned. (us, California)

Quick background: Father in law died in March of 2023. He was with his girlfriend C (77) for about 25 years but they never married. The second house on the property became vacant in March 2023. We visited C to help fix up the second house, and after some discussion with her decided to move in and sell our urban house. She has been charging us $1200/ month from the time we moved in in October of 2023. This is a fair to high price for the area, which is very rural northern California. She could have had a tenant instead of us to earn rental income, as she is accustomed to. EDIT TO ADD She has owned 2/3rds from the time they bought the property, FIL didn't leave 2/3rd to her.

Issue we need advice on: We DO want to contribute to the property, but we feel taken advantage of with the rent situation. The property is 77 acres, half wooded, half pasture, with two houses and a barn. It cannot be subdivided legally because of it's agricultural zoning (each parcel must be 40 acres or more to subdivide) so we only own 1/3 on paper, not a physical 1/3. The property is paid off and property taxes are $6000-$8000/year. We don't know the real number because she keeps all of that information from us. She wants the rent in cash only, with no contract. I asked if she would take a personal check and she refused. She recently told us she only has $1000 saved to put towards the property taxes, hinting that we would need to help her cover it when the time comes. She also doesn't let us use land away from our home for personal projects (gardening, animal raising, etc.)

When I asked her about our (my husband's, really) ownership of the property, she said she has "sovereign" control. By this she means that we have a landlord/tenant realationship.

My husband inherited his 3rd of the land through a trust from his father. We did go to a lawyer and get my husbands name legally added to the deed. Because we moved onto the property within a year of my father in law's death, the property didn't need to be reassessed (yay). At the time we didn't bring any of this stuff up because we were still grieving and hoping C would be reasonable. This lawyer is available to us for $700/visit and we are willing to go back to her if we feel we have a case.

Do we have a right to not pay her rent? If we don't pay rent, she has lost out on income she could have earned from a regular tenant. Also, how should finances be handled in this situation? Do we pay 1/3 of the property taxes and 2/3 of the expected rental income? Is this something a court should determine case by case?

About the tractor: My father in law bought a new tractor about a year before he passed. C thinks it's too small and wants to trade it in for a larger one. Our issue with this is that we think (but don't know) that the tractor belonged to my father in law and C has no ownership of it. We do not hold the physical pink slip so we can't know for sure, but his (FIL's) friends told us it was ours. Our worry is that she will trade in the tractor and put her name on the slip. Can she do this if her name isn't on the original tractors slip?

Thank you for reading. If you need any clarification please ask.