I need to replace a cv axle boot on my mom's car. Ive seen ones before that are split in middle. Are you supposed to glue those together with something or how do they work?

Those came with with a bonding agent and ties to keep them together for the glue to set up....

which ones should I go with? It would be easier to install glue-on ones but if theyre not perfectly glued they would leak grease.

Only use a screw- or glue-together "split" boot if you are not removing the shaft. They should be considered a temporary fix- they do not last anywhere near as long as a 1-piece boot.

If the boot's been damaged long at all, all the grease will have been thrown out, dirt will have gotten in- and the joint is (or soon will be) history. Check to see if the grease feels gritty. If it does, replace the joint or shaft. If the shaft makes any noise (clicking on turns, clunking, etc.- removing and replacing it now would be the best bet, IMO.

If the boot just got damaged and wasn't driven any distance, a one-piece replacement boot is always better than any of the stop-gap split boots. But better still is to just replace the shaft and be done w/it.

i agree with cobalt.
the split boots don't last.
IMO, replacing a C/V boot is a waste of time. if im pulling the shaft because of a bad boot, i'll put in a remaned shaft.

I went ahead with whole boot, Ive removed old one and now Im stuck trying to remove outer cv joint

Ended up replacing whole axle