Tell “new elderly member of the household” they can live with your rules or live somewhere else. If that’s not good enough, let them get their own service on their own device that can’t be seen or heard by anyone else.
I’m with you on that. A parents first responsibility is to the children. If a grandparent is bringing bad influences into their lives then it’s up to the adult to protect them. This happened to me. My father would put on raunchy DVDs when we came to visit and I put a stop to it. My brother actually pulled me aside and thanked me. I wondered why he stood there and let Dad do it.
To the OP. Keep the whole house TV off, the other poster is right about commercials. Get grandparent a laptop and a subscription to SlingTv or a digital antenna just attached to their TV.
Some situations are not cut and dried.....some elderly parents are very sick, bedridden and or in hospice. It may be the last few months on this earth. I chose to make my mom comfortable and happy. If that meant she wanted cable and a variety of viewing options, then so be it. No my house my rules in that situation.