i would put the 4 small corys you have along with the 4 cherry barbs in the 10g. this might be a tad overstocked, but provided you do regular water changes and maybe add a plant or two if possible, your tank should do just fine like that.
maybe try a betta or something in the 5g with some ghost shrimp? you *could* add a couple a peppered corys to the 5g as well after it cycled if you approached it in the same way as above. you also could try the all ghost shrimp extravaganza proposed by sumpin' fishy. i have read that they can be bred in a small tank like that with a sponge filter, as a power filter will suck up the babies, but i haven't tried this myself.
i'd also maintain that ghost shrimp really don't add significantly to the bioload, and you could probably add a couple to either tank in addition to those fish, no matter what you choose.