Hi,
My dd is quite the wiggler. She's 9mos, sleeps between me & the edge of the bed, and has rolled out exactly once. Since we have a fat, firm pillow on the floor in that spot, there wasn't a problem (except she was pretty disgruntled that her rest was disturbed!). I believe that like every other healthy human, babies have an instinct for where they are when they're asleep. If you don't have soft carpet on the floor by the bed, get a firm pillow & lay it there, that way if your babe takes a few "learning tumbles" there won't be any harm done.
Really, the bottom line is, this isn't your inlaws' baby, it's yours. You don't have to justify yourself to them. If you feel that in your bed is the best place for her, then have her in your bed, and let your inlaws know it's not up for discussion. Same with the cereal
they're telling you. There's a wealth of information here on both topics if you want to ease *your* mind, but you don't have to ease theirs.
I hope your husband/partner is backing you up on this. I really think that if a partner's family generates a lot of flak, it's their responsibility to run most of the interference for you.
Good luck, enjoy your baby, and listen to your mama instincts!