Was last time their 1st litter? It is not uncommon for gliders to lose their 1st litter, they are more careful with the next ones.
You should not remove the joey from its parents unless you notice something is wrong (young joey crawling outside the sleeping pouch or left alone for a long period of time, joey crying without getting attention from its parents for more than a few minutes, injured joeys or clearly underfed), in which case you would have to either supplement feed. or hand raise.
In any case, separating the father is not a good idea as both parents take care of their joeys.
Here are some informative pages about care of rejected joeys and hand raising :
rejected joeys :
http://www.suzsugargliders.com/helpforrejectedjoeys.htm
Hand raising :
http://www.suzsugargliders.com/handraisingajoey.htm