I would buy two traveling playpens and have them sleep in those. Bring your own blankets, sheets, etc. I would travel at night, when the twins are most likely to be sleeping through most of the car ride if it's a long distance. I'm not sure how old they are, but you can use a car DVD player to entertain them a little during the ride when they're awake; if you don't have one, you can probably borrow one from a friend or relative. Plan to make frequent stops if you're traveling in the day. When you stop to eat, let them play around a little on the grass or something. As far as what else to bring, just think of your daily routine and what the necessities are. I'm not sure how long you're staying, but grandma probably has a washing machine, so don't over pack because she probably won't mind if you use it. Bring some toys, their favorite thing to sleep with, feeding supplies and 1 high chair or equivalent to feed them in (they can take turns eating in it since the car will be too full if you bring 2 high chairs.) If they sit up, you could just bring Bumbo seats and feed them in that. Of course, don't forget any medications, Tylenol, teething tablets, whatever-that will make your life easier if something should arise. The biggest tip I can think of is to bring baby proofing devises. If there are not kids at other people's houses, (and when we go to a hotel) I always bring the light plug covers, an adjustable gate, etc. When you get there, get down to the ground at their level and remove all the breakables and dangerous items within their reach (with grandma's permission). On Halloween we went to eat at my sister in law's house before trick-or-treating and I didn't know she had candles lit on the side of her couch. Sure enough, he went over and put his finger in one. It didn't leave a mark, but my point is, I wasn't even expecting that-she's never had them on before when he was there. We moved one obvious candle in the center of the room, but I didn't see the other one. Bring the stroller in case you go places, baby monitors if they won't be in the same room with you, diaper bags, bibs, etc, etc, etc. Oh, and a kids music CD to entertain them in the car. I usually bring a happy, playful one and a sleepy,lullaby one.