You don't have room for any more top-dwelling fish - certainly not gouramies anyway.
Bettas do not do well with gouramies long-term and gold (three-spot) gouramies become very aggressive with age. If you don't think about finding new homes for the betta and golds soon, you're going to have serious problems - probably deaths.
Because gouramies are territorial by nature, each should have around 10 gallons of territory. That means 2-3 gouramies max. in a 25 gallon. This guideline can be applied to most of the common gouramies - such as your dwarfs and golds. Bettas also need a good amount of territory if you want to keep them with other fish - but they shouldn't ever realy be kept with other gouramies.
What I would suggest is for you to get your betta his own 2.5-5 gallon tank. Use mature filter media or gravel from your existing (and hopefuly cycled) tank to avoid ammonia spikes occuring when you add him.
Then return the gold gouramies to your LFS. Though you have not mentioned what sexes they are, I'd be extremely worried about them becoming significantly mroe aggressive in future and, in these crowded conditions, killing (directly or indirectly) their tankmates.
The dwarf gouramies would be fine left in this tank but you shouldn't add any other gouramies at all. What you can consider is small-ish mid-dwelling schooling fish such as harlequin rasboras or black phantom tetras and a handful of bottom-dwellers such as cories. A trio of some kind of smaller livebearer - such as platies, guppies or endler's - would also make a fine addition.