When you feel like an intruder in your own home I think it is time to have a serious talk as to what is and isn't acceptable behaviour from your "guests" - they may be family but they are old enough to fend for themselves and should, I think, be seen as guests.
As someone else suggested, counselling too may help you to be more assertive and able to deal with challenging situations.
What do you find yourself avoiding more as you get older?
