Eck - my first advice would be to ignore the advice that says you have to take your child with you everywhere. If that works for you, great, but in all honesty, it's just great that you're working so hard to give your son your own milk, and you shouldn't be made to feel like you're doing anything wrong by wanting to leave the house occasionally.
Secondly, like everyone else has suggested, try out some different bottles & nipples. The ones that worked for my son were the Nuk bottles with stage one nipples. The flow was slow enough to be similar to mommy's, and the shape worked for him as well. I tried the fancy ones that are supposed to be just like real nipples, but those didn't work for us. Have you tried giving him a bottle yourself? Maybe he just wants to be close to you, rather than your hubby or MIL. If that's the case, once he's used to using a bottle with you, it may be easier to transition to having him fed by someone else again.
Good luck! And congrats on sticking with mommy-milk as much as you have.