I find myself becoming irritated with my Mother at times. She's a truly lovely person and would do anything for those she loves, but lately she's been getting on my nerves - and for reasons which aren't 'new' or 'sudden'. For example, she constantly interrupts and talks over people - and she'll enter a room already talking over you. It doesn't matter how many times I make a joke of it ("Oh, that's fine, I'll stop talking while you interrupt", or "No, no, carrying on interrupting").
I think I'm getting older and grumpier, so I'm just noticing it more than before.
I try really hard not to become irritated by her. There's some comfort for me in the fact that my sister also notices it, so we can roll our eyes at one another.
I ALWAYS feel guilty for being annoyed with my Mother.... which irritates me even more!
Can you get through visits with your Dad and Sister by being sarcastic? I do have a good relationship with my Mother, so can say stuff like I've suggested above - and she'll laugh and call me a cheeky cow..... and then five minutes later, she'll do exactly the same thing again. She also constantly talks about people I don't know in minutiae (Barbra's cancer, Jeff's colitis, Carol's son's wife's sister's angina etc) and repeats the same stories..... but I think all Mum's do that, don't they? My Grandmother (my Mother's Mother) is exactly the same - if I've heard the story about John up the road having oesophagal cancer, having to have a tracheotomy and not being able to enjoy curries anymore once, I've heard it twenty-five times.
I think you have to get through visits with your Dad and Sister by employing your own good humour.... and finding someone to share the irritation with!