Yeah, I completely understand...Thankfully in our case, my stepmother's kids are not involved in what goes on BUT I still have to deal with her...which is like walking on eggshells. She is a lot like S is to you, Diana...altho she and my daddy ARE married...Well the fact is, we may jointly have to make decisions for our parents in the future, so I think it's important that we are on good terms. For example, if it becomes necessary that S move to an assisted living place, and S wants Dad to come with, or vice versa, I don't want to have to deal with her kids' resistance to paying for Dad to stay with her.
I think it's better for Dad if I smile and nod and deal with them, and work harder than I should have to, in order to have a workable relationship with at least D.
She keeps tabs too of everything. And is very much based on appearances not being a REAL person.