For sure, the previous owner was just a mug with more money than sense
You'll definitely be able to sell everything on though, just check the voltages on the lipos to make sure they are in good health.
Your Sigma II EQ Lipo charger is much more modern though- you don't need to do any special wiring to charge your lipos on that; just plug the main power leads into the main power leads coming from the charger ( red & black, may need charger leads with a male traxxas connector like so:
Clicky ), then plug the white balancer connector into the balancer board that is connected to the charger; seems like the previous owner chose the awful Polyquest style balancer connector so you'd need a PQ balancer board for your charger in order to connect up the minamps lipo for the time being ( most lipos these days use the generic JST-XH balancer connector that comes as standard with most chargers too ).