It does look a little wrinkly to me. Does the mum have milk? She could try holding the babies to mum to feed... support the mum in a sitting position and latch the babies one to feed one at a time.
If she's got some accurate scales weighing them now and again in 24hrs should show a difference. Dehydration is the first issue if not, so feeding them a little plain boiled water (cooled) in a clean syringe will tide them over without upsetting their tums like substitute milk.