I would start off by keeping him close to his same schedule. If you find he is willing to adjust, go for it. Beware of family; they probably won’t let him sleep! We went to visit family on Easter weekend (4 ½ hour drive

) the only time I got to be with our baby is when she needed to eat or during the night when she was sleeping.
The plane ride should be ok. You can feed him or change him whenever. In a car they are confined to the car seat and have to wait until you can stop somewhere. Are you breastfeeding? I have heard that breastfeeding during takeoff and landing to help relieve pressure. I’m not sure if it works for bottle feeding, the sucking might not be strong enough.
For the plane ride if you are formula feeding you should get the ready made formula in small cans or bottles. They even have some that all you have to do is attach the disposable nipple it comes with. That way you can keep it at room temperature and you don’t have to worry about keeping it cold or warming it up (hopefully he take room temperature formula). The ones with the disposable nipple you can just throw away when you done, no dirty bottles to deal with.
Bring some of his favorite toys or books to keep him occupied and anything you think might make the flight easier. You should be the first to be able to get on the plane, so you will have first dibs on the overhead storage! It will give you time to get organized and ready before everybody else gets on. Good luck!