How to start breastfeeding at 5weeks

Jen
I have 5week old twins. They spent time in the nicu and we currently bottle feed breast milk and supplement with formula.  I'm trying to start to do more breastfeeding but my son and daughter fall asleep after 10minutes or my daughter seems to nibble instead of feeding .  We end up supplementing with a bottle of formula or expressed milk. I need advice on how to get my twins to feed at the breast more so I can eventually cut out bottles.