I have some old sibling cats 2 fe and 1 ml all inside cats well they pass at the same time?

There is no reason to believe they would all die within the same year. Average life span for indoor only cats who do not have health and dental issues and who receive consistent vet care is 15 to 18 years with some living to 20. I had a mom, lived to 19, son who lived to 17 and daughter who lived to 16.

It's possible, but we can't tell you for sure what will happen. Odds are against them all passing within the same year. The average life expectancy for male indoor cats at birth is around 12 to 14 years, with females usually living a year or two longer.

Not necessarily. I had two sisters and one lived to be 15, the other 18.

Probably not. They may end up dying a few months from each other or one or two may live years longer - no predicting when they will die.