Soaking wet diaper during the night.

So this is the 3rd night on a row that my 18 month old son soaks his diaper so much that it leaks and Wets him and the bed, and this is extremely annoying because 9 times out of 10 his twin sister will wake up since I have to change him, flip the mattress and change the bed sheets in the middle of the night.

Can my mamis here please give me some advice on how to stop this? He sleep on his stomach so that’s another thing.

They use overnight diapers, I change him before he goes to sleep (and also do it over night). He does drink milk (9oz) right before he goes to sleep but I try to cut off liquid an hour before bed time (no water nor juice).

I NEED HELP 😫😫😫😫😫😫😫😫😫