How do I deal with a sibling who has given me nothing but grief and emotional drainage over the years and says sorry but is moving too fast and making decisions on visiting my stepdad while I am caregiving for him and wants to come over and make a family dinner?
Your situation doesn't seem as extreme as my experience but it can turn into it especially if the other family members are only interested in your Dad's bank account.
I can GUESS what you might men, as I'm a caregiver to my mom, who has dementia. My siblings don't visit or call but they all live out-of-state. A card or phone call to mom would be nice and I've asked them to contribute that but, no. I'm in this by myself and I could be resentful but choose to keep mom happy as possible. It's all about her care, safety and happiness. That's the focus.
I always believe that parents usually play a role in siblings not getting along, so it's best to protect yourself from the negative energy. Your stepfather has two children, but you are alone in this situation. Don't rise to the bait. Try to be civil but remember that a tiger doesn't change its stripes. You are not obligated to be anything but civil. You probably can't restrict visitors so you will have to make the best of a bad situation.