What era/s are they from? I am not an expert but I kinda sorta collect them (using the term lightly as I mostly just buy ones I think are pretty second hand and occasionally go after clothing for them online - but I've done bits of research here and there). From what I can tell, it can be pretty hard to profit off 80's and up dolls (I don't really like Barbies older than that so I have no clue on them) though there could be some choice rare ones I don't know about! I imagine if you have their outfits and they are in really nice shape, you may be able to resell some for a little more than a few dollars.
I have sold some newer Barbies with success - people seem to really go for the ones with the Model Muse type bodies.