I'm sure his parents are aware you have sex, you're adults and it is a perfectly natural thing. I'm sure his parents still have sex, and they are fully aware it is a bond building part of a relationship as well as for pleasure. Could your boyfriend perhaps ask them if it could be aranged to have an evening in by yourselves for some quality time, he doesn't have to expressly say "we want sex without worrying you'll overhear/walk in" but i'm sure they'd understand and be happy to go visit a family member or have adate night out together to give you some space.
Once that's sorted, what helps you to relax? Grab some candles, scented make for a lovely atmosphere, and the type of scent can set a certain mood, be it relaxing with things like lavender or sage, or a more spicy cinnamon for a flirtier mood. A bubble bath, a massage with a nice oil or lotion, then some extended foreplay, concentrating on the none penetrative ways to please eachother, sensual over sexual, and should you feel confident or comfortable and in the mood to take things further, take it slowly, maybe try a position with you on top where you control depth and speed for some added confidence.
It may be worth having a browse for either a silicone or anal lubricant, they can be thicker/more moisturising than a standard water based (the water based anal lubricant would be more suitable if you use condoms to make sure there's no degrading the latex) or maybe build up with a few size incrasing toys to relax and prepare yourself for sex if he's a girthier guy.