i am installing a mobile gmrs radio in a jeep and i also have a cb. can the antennas be mounted on each rear corner, one on passenger rear corner and one on the driver rear corner
Yes, that's plenty of separation between antennas.
One of the issues with Jeeps Wranglers is that installing antennas on them can be a challenge.
CB's are pretty forgiving. You'll see a lot of people just slap an antenna on the rear quarter and call it done. If you check the SWR, often you'll find it's high. Often this is related to the lack of ground plane under the antenna, or a lopsided ground plane. It can be made to work just fine, but sometimes you'll have to put some work into adding additional ground straps to the antenna base, rear tailgate, doors, etc. Making sure you have a good RF ground between the antenna base and the body, as well as between all the panels is important.
UHF is a bit more forgiving since the necessary ground plane will be smaller. Still, mounting a UHF antenna down low on the rear quarter panel can create some shadowing from the body. You may want to consider a 1/2 wave UHF antenna, as they'll work without a ground plane.