If I were you I would take your youngest one to the dentist (how old is he?) and see what he recommends. There are different degrees of lip tie as well. Also I would get him checked for the posterior tongue tie.
Dd's upper lip is always curled in and she has a very shallow latch. It took a while but we figured out how to nurse around it. If it becomes a problem in the future I fully intend on getting it clipped, but for now I feel she is too young (5 1/2months) to be put out under anesthesia. But i didn't take her to the pedi dentist. Here's what hers looks like: