My FSIL gets married in a couple weeks and just invited us to a post wedding brunch at a restaurant. Invite was casual via email but there was a request for an RSVP and reservations made at their favorite restaurant (which is pretty spendy). My FI and I obviously will RSVP and go but I just don't know what to expect. Is this a formal invite and we can expect them to host the brunch or should we plan on paying for anything we eat and drink? This makes me anxious and am completely not comfortable asking the B&G what to expect and apparently neither is my FH. $$ is tight for us as we are planning our own wedding and already have spent a mint on their wedding... any words of wisdom?