Getting toddler to sleep

Tips for getting toddler to sleep through the night? My son is almost 2 he shares a room with his big sis (4yrs old) she sleeps through the night but he has been waking up crying every night 1-3 times through the night and is up at 5-5:30 am... He goes to sleep fine but I have to lay in bed with him until he is asleep. Currently it’s been very draining dealing with this on top of getting up often through the night with our 6 week old baby. He’s been waking up our oldest too due to the crying so that’s been challenging also. I have a routine EVERY NIGHT and we stick to it. (Upstairs at 7:30, pjs, 1 book each, we read, snuggle, asleep between 8/8:30) they use a sound machine and the last few days I’ve been trying a lavender diffuser. He does nap during the day. Goes down around 12 and sleeps about 1-2 hours. Any advice or other ideas that might help him sleep better would be great.