Since they are new gliders I would take them to a vet and get a check up.  see 
if they have any illness.   that is your BEST, FIRST STEP.  
    gliders groom themselves and each other.   one glider is a ALPHA OR LEADER OR 
colony BOSS MAN.  This is natural, drop the thoughts of bullying.   My alpha Gus 
will sometimes chase, nip at or look like he is attacking another glider.  there 
is no injury and seconds later they are fine, sitting together with me.  
     BUT you need to keep and eye on them, feed them good food and have playtime 
and things for them to do, sometime gliders do kill cagemates, but some over 
grooming might not be a big deal, so see the vet and get some good information  
from a professional please.