When do we start talking assisted living or nursing home?

Wife and I sold house. Bought a motorhome and put it in her dads driveway. To take care of them. Mom is 82 dad is 89. In December mom was diagnosed with stage 4 lymphoma and is now on treatment. Since she started treatments it has also affected her mind, forgetting things not doing things that she normally would do. That's okay except for my wife has to be there all the time to reminder. Dad is no help for he has his own physical problems. She forgets to take her medications and treatments for breathing and when I asked will lie about it. She has forgotten how to do the little things like turn on the stove ,turn off the stove etc. M wife cannot live in the house with them for their growth very hard to get along with at times. This is also affecting our relationship. How do we start the process of taking them to assisted living or nursing home. Who knows how long my wife can do this and she's worried she is going to end up resenting them. When we first moved here dad was treating my wife like a maid. She finally set him straight but still has a tendency to regress. We are willing to do this for a couple of years but not willing to give up the next 10 years of our lives for these people. Mom also has dementia.