Should there be compensation for partner’s mother’s care?

All three of the suggestions below mine have excellent points; it is time to sit with family and discuss all of this. For starters I would never assume this care for anyone, no matter how much "free rent" I got, nor no matter now "compesated" by renting out my real home. You have chosen to do it. Dependent on Mom's age you have decades ahead doing this, and it will become the only job you are capable of handling, IF it can be handled 24/7. It may be time to share Mom out with other siblings. It may be time to discuss compensation. Be certain you have a care contract well written by a lawyer in your state, and that you claim the compensation under taxes, so that this doesn't fall under "gifting" should Mom need care in future and outlives her assets. This is really an individual decision of what you are willing to do with/without compensation and for how long. Family should be informed and working with you, and attending yearly update meetings as a family to discuss what page you are all on. If argument continues I would place Mom in a good Assisted Living where her assets without any doubt will go to her care. And where quite honestly she will be less a burden and may have more a life with friends.

If she can't care for herself, neither should she be left alone. Dementia is very unpredictable. You never know where their mind is andvwhat they are capable. If the Caregiving is getting too much, then siblings need to be told outside help is needed. No one should be expected to care for someone 24/7- 7 days a week if there is money to lighten the burden.

If your Mom starts to fail, she is your first priority. If partner needs help, then he hires it using Moms money. Who has POA? I hope your partner. I would never Caregive without having the ability to get to the money or talk to Doctors.

Concerning u being paid, I think you should be compensated for your time. But then, you are a spouse not a friend and usually spouses don't get paid.

I see both sides.  Yes, in general, caregiver should be compensated, but very few family members are.  And I see their point re the rent.   I know of NO unrelated live in caregivers who are allowed to have a spouse live in with them, this does change the dynamic.    IMHO, one issue can be that siblings remember how mom was a few years ago, when she did not need much help.  Every year, this will get worse.   Even if she can be left alone now, that will change in a few years.

If you do get estimate of live in help from an agency, I do think you have to consider the rent issue. 

How you and your partner share or don't share money is between you two, but is an issue.

Yes you both should be compensated for the caregiving you are doing.
No rent or "room and board" can not be used in lieu of payment.
You can not get "back pay" for the past 3 years but you can start now getting paid. Check a few of the agencies in your area and find out what they charge for 24/7 care. Write a contract and figure what each of you contribute and how much each will be paid.
This may become more useful if or when there needs to be an application for Medicaid or other support. The money that is paid to the both of you is spending down her assets. (If your partner does not want the money he can put his portion into an account and divide it with his siblings later. For your sake keep your finances separate)