You poor man. In trying to protect and please everyone, you are pleasing no one, including yourself. You really do need to get out of the middle of the conversation that your father and your wife are having through you.
The first consideration is the personality and confidence of your daughter. Some 12-year-olds are far more ready for this kind of adventure than others. Does she want to go? Is she comfortable with your dad and does she enjoy his company? Is she able to take care of some of her own needs (like making meals) if your dad’s back gives out? Can she entertain herself if your dad either isn’t up to entertaining her or doesn’t really know how? Since his home is isolated, is she happy to be her own company? Or will she become quickly bored without other kids around? Most important: Is she the kind of kid who can assert herself? If she doesn’t feel comfortable, will she call you and her mom?
This is not to suggest that your daughter make the decision. She shouldn’t. It’s unfair to ask a 12-year-old to make a decision that the adults can’t make. The three adults – you, your wife, and your father – need to make a careful assessment of her readiness and her interest in a visit before making a decision either way.
Then, encourage your wife and your dad to join you in talking this out. This situation shouldn’t turn into a test of who you love best. You love them both. Nor should the decision be based on some idea of “fairness” in visiting grandparents. Fairness doesn’t require that everyone be treated exactly the same; only that both sets of grandparents have the opportunity to know and love their grandchild.
It’s understandable that your wife would feel more comfortable having your daughter at her parents’ home since there is a woman in the house. Your father’s disabilities also need to be taken into account – both in terms of what he is capable of doing and in terms of how his behavior affects your daughter. Your wife’s concerns can best be answered by your dad. Your dad’s reassurances are best heard directly by your wife. Remind them that the most important focus for their discussion is what your daughter is ready for and how you will all help her have a relationship with her grandfather, regardless of whether she makes a visit this year or sometime in the future.
I hope you can all move your discussions and, indeed, your relationships to a new level.
I wish you all well.