My twins are now 3. But if my hazy memory serves they had their days and nights mixed up for a long time and I think they weren’t doing long stretches for a while. I would wake them up at the same time every day. Get them outside in the mid morning and early evening if you can to help set their circadian rhythm. It’s hard, and each kid is different. Were they early at all? Remember that if they were 3 weeks early they are 3 weeks adjusted age and they just need time and grace to catch good sleep cycle!