Tiger barbs and 1-2 female bettas?

I don't see why you couldn't.. The only problem I would see is the two betta's. I had a 46 gallon bow front with like 25 tiger barbs I it and had a few different tetras and a placo and a few loaches so I dont see why the betta's would have any problem surviving at all. That and you said it was an established tank so I think you will be just fine