I was going to suggest music too. We have it on from bath time onwards to soothe their minds for sleep time. Another idea might be to separate them for going to sleep if you can. So little one first then 20 mins later older son goes to bed. He might be able to lie in your bed and rest with some books or something? We had to separate our two for a few months then gradually were able to get them to sleep together again. It was used as a special treat so if they didn't sleep well together then they would go back to separate bed times the next night. Bed times are so hard with lots of little ones - good luck!