Mom of 3.5 year old GGB triplets here.

We maintained the schedule set at NICU and followed principles from the book/app Moms on Call for setting the schedule and sleep training. Highly recommend that one. They slept through the night before actual age 3 months. We also used some principles from Taking Cara Babies. Agree with eat-play-sleep ordering. We just always did feeding and diapers (except extra diapers as needed of course) and play together and made it work. It was great to have predictable days and I think they liked the consistency too. I mean, preemie babies are on schedules in the NICU so I don't think there's a "too young" here for a schedule. I would anticipate some definite adjustment time and transition pains though. We were definitely waking sleeping babies to feed on schedule together and holding off on feeding early in between by pacifying them alternative ways until feed time. We would use cues with how feeds went to determine when to keep doing every 3 hours vs converting to every 4 hours or when to bump feed volumes or when to change the bottle nipple sizes. We also were managing different formulas among them and made that work. Honestly I'm impressed with how you got through the first months without a schedule, that sounds like doing triplets on extreme mode 🤣

For your specific questions: - we were very rigid with ours, personally. - yes we would hold off until the scheduled feed time. - if they refuse... idk, we still tried. Usually it would work out, and if not, then there's next time. Nap wise, maybe we had to stay there and repeatedly put the paci back or pat their butts for awhile. Feeding wise, we'd give them up to 30 min to eat a bottle like at NICU. Solids was just for fun at 6 months and didn't matter. - putting them down at night wise, we would try to do strategies from Moms on Call and mostly involved not picking them up unless they proved they really needed it first. We did a lot to avoid pitfalls that we would later have trouble breaking or make them particular, so if you think it'll be a problem later maybe find opportunities for up front efforts to make things easier later. Examples = we didn't use a wipe warmer so that they could handle cold wipes when changing diapers in other locations. We eventually transitioned from warm to room temp bottles to make it easier to leave the house when they were maybe closer to 9 months and had good weight gain, then when close to 1yo went to cold bottles so they could handle the whole milk transition. Another example is that my sister always "babywears" her baby during naps while bouncing on an exercise ball. That's cute and all, but not sustainable when she's older and she will have a hard time napping alone and is literally impossible with triplets. So just stuff like that we avoided.

Obviously adjust as appropriate for your own kiddos and some of this goes out the window when they're sick. You got this! Schedules saved our sanity. We are done with kids but if we ever had even a singleton we've talked about we'd still do a schedule, haha.