Let me assure you that your babies are of not much lower weight than normal.
Low birth weight
(LBW) is a general term for babies with birth weight less than 2.5kg. But babies gain weight as their intrauterine age (gestational age
). For 34 weeks twin baby, the average weight would be around 2040 gm.
I would prefer to start with mother's milk only from birth as that is sufficient and most appropriate for your babies birth weight category. Mother's milk is always the Best thing for your babies than Formula feeding.
Breast Milk secretion increases as your babies are breast-feeding, and decreases if they are not sucking. So, to maintain breast milk flow continue breast feeding. Breast feeding should be continued till 6 months of age.
However, your doctor may have found some issues in your babies (Sorry, I don't know). Discuss with him / her for that. If no problem is there, start breast feeding - IMMEDIATELY.