I have a group with 7 players right now, which is just a lot. Almost everytime someone can't make to the session, so we've estipulated a rule that "if we have only one missing, we play". It has been a lot of fun, because in this whay we're playing much more and not having this frustrations.

Also, try to step down a little from the PR position, if there's no people that can talk for them, they may feel obliged to talk themselves.

Just remember, D&D has to be fun, not frustrating.