atiel feeding problem, Avian Vet please help me!?

An avian vet can help you by examining the birds, and testing for disease or problems. Yes, it is expensive to go to a vet, but it is a responsibility of pet ownership. If they are baby birds, they may not have been fully weaned, so you can buy some hand feeding formula and try to feed them with a little spoon. I don't understand your statement about them being rare brother sister twins. Did they come from the same egg (RARE), or are they clutch mates hatched at the same time (not rare at all).