First give the breastmilk. If still baby is hungry then give formula as much quantity as baby takes. Breastfeeding and breast milk is preferred over formula. As this is twin case, can consider formula if milk output is less. If giving formula, them give only by pallaida and not by bottle, as bottle feeding can cause nipple confusion
Next Steps
As u gets practice, and in many cases, even for twins many mothers will have sufficient milk products by 3-4 months.
Needs History regarding adequate feeding
Health Tips
Try giving breastfeeding as much as possible. As nothing can replace it.