@Freida - my best wishes. You know s family member lives with us and while that relationship has complications even straightforward situations - with us - it’s not easy .
We have some ground rules in our house - when people are in their bedrooms - in day time - they are not to be disturbed unless they say - I’m going to bedroom but I’m available. Sounds formal but it’s really useful boundary setting. Not just for ptsd but for safe smooching or watching a non PG rated movie if you have a kid in the house now .
I also have a schedule that preempts my window of tolerance and allows for others’ issues . ( it’s not only my mental health that counts. Right? ) Just knowing what needs others have and having some schedules that can be reviewed for and high pressure areas ( any shared bathrooms/ kitchen / cooking duty - ) and agreement over what constitutes ‘fair shares’ of doing stuff, so everyone feels included , no one taken advantage of etc.
you are a good sister /aunt and a good human for doing this as is your partner