Awkward invites

[Leapers]

Hi everyone,
Just wondering what the social etiquette is for my current situation...
I am in a long distance relationship with my boyfriend at the mo but he is coming back for a short period over easter as its both his mothers, fathers and sisters birthday in a matter of three days. His mother has been ill recently and had time off work due to a severe allergic reaction to some prescribed medication (although the worst is over) and has invited me to her birthday meal, it is classed as a celebratory meal as several of my boyfriends siblings have just qualified, got new jobs, etc and i have also recently had a new offer.

And this all seems nice i live a good few hours away from his family and although i have met them all a few times they're all lovely, he does have a huge family, he is one of 10 children plus all the cousins and other relations which are invited, they also slightly intimidate me due to being from a very small quiet family, I am not sure whether to accept the invite it would involve staying for a couple of days with them and if his mother is just recovering would i be more hassle to her health.
I am also the only person invited that is not an actual relative which i think puts some pressure on me, and i am not the most socially comfortable person and find it awkward to chat to so many people at once.
I am not sure whether to accept the invite and man-up a bit or decline politely with other work committments or something? Would it be rude?

Thanks