Drive Train help

[Samk]

Our team had decided to use 8 wheels, all of them 8 inch andymark wheelchair ones(non pneumatic), as to be able to turn, the center 2 on each side were supposed to be lower by .1 of an inch. Some mentors brought up a concern that we would be too tippy with this design, we were under the impression that this is common to do. Any thoughts on whether to drop the center two or not? Also, we got all the blocks mounted, and found that though the shafts were true, most of our wheels had significant wobble, and they are brand new straight from andymark. Any thoughts on how to combat this? as it seems to cause major problems when chain is put on.