At 34 weeks preterm, babies usually sleep most of the day and night, waking mainly to feed, so the long sleep stretches you're seeing are expected at this stage. Milk coming back up through the nose or mouth after feeds is ordinary reflux and usually settles with time.
Next Steps
The lip or tongue movements, falling asleep suddenly after crying, and the eye-closing after a multivitamin dose aren't things to call normal without actually seeing your babies, since preterm infants need an in-person check for this. Please get them reviewed by your paediatrician, who can also guide you on milestones given they were born early.
Health Tips
Get them seen the same day if any movement looks repetitive or jerky, if breathing or feeding is affected, or if they're unusually hard to wake.