Best situation for a parents cat left alone alot this summer?

My dad will be gone up north 5-7 day trips about seven times before October hits. Last year they put there 11 year old cat to sleep as she kept wigging out when they would go to the point she kept defecating on the bed every time she saw luggage. I saw that coming a mile away as I would be the one left to check in on her and she started hissing and completely wigging out from the situation last summer, they were gone too long and too often and just dont understand cats well. He recently took my sister's Siamese 2 year old as she felt she had too many animals. This is all against my better judgement and I actually stopped talking to them for a week as I was mad how easily my sister could get rid of the cat she wanted so badly and that I felt my dad would be better off with a dog. He is good to the cat and she follows him around like a shadow. I never seen a cat need so much attention all the time but as I warned my sister the day she was going to get her I heard this breed is high maintenance. I just dont want a repeat of the previous cat. He claims he does not want her to go back to my sister when he is on vacation, that it will confuse her and she will come back more whiny. I figure even if I can stay with her six hours a day it still will not be enough, taking her up north not good idea, long drive and all those people she will easily find herself outside from a door not closed. I have small apartment and will not risk upsetting my male cat. Dont you think the best scenario is going back to my sister where she spent a year and half as long as her cat and dogs treat her the same for few days?