I was worried about feeding in front of my dad, but he surprised me by being totally unfazed and even coming out with supportive comments. I don't know why I worried, my mum bf me and my sisters. My mum bothers me more, I don't think she means to, but I feel really watched feeding front of her.
Mil's husband always seems uncomfortable, but he always seems to find something that needs doing in another room when dd needs feeding! I use a muslin to cover up, but I do struggle to feed discreetly. I'm not sure dd's head is bigger than my breast at the moment!
I just played it by ear in the beginning, you'll soon find out what you're comfortable with, or not. No one would be offended if you wanted to go to another room to feed your baby.