Hold the tips with a pair of pliers and apply heat to the tips while pulling on them with the pliers. When the glue heats up enough it should release and allow you to pull tip and insert out of the shaft. You will have to get more inserts and glue them in the shafts if you can't get the inserts to break free.
It sounds as if the metal in the tips and the metal in the inserts have oxidized and are kind of wielded together.
I would try heating it a little and trying to screw them out before trying to remove the insert. If you get them a little warm maybe the metal will expand a little and let them come free.
use bees wax on threads next time. old style string wax. hope you got them. be careful with the heat.thats the way the shop removed mine to cut arrows down an inch.
welp, lost the first arrow, heated on the stove, and it got hot enough to twist the arrow, and it broke off just below the insert. so im just gonna save my other one as a practice arrow, and have to buy a few more before season