You Pediatrician will say they are tall.
My kids are tall too. Not 'as' tall as yours, but close.
My kids were born at 21" long
Currently, my 4 year old son is about 45" tall.
My Daughter is 8, and she is 53" tall. So that is the same as your other son.
Both my kids, are tall... and lanky. Not 'big' in girth.
Mind you, in my Daughter's Grade Level (3rd grade), MANY of the kids, 8 year old, ARE my daughter's height, OR taller. Her grade level, is FULL of tall kids. My Daughter's friends, are taller than her. For example.
My kids have always been in the upper percentiles too.
Our Ped, has never said it is problem.
Just this past year, they have grown.
My Husband's family, are very tall people. My Husband is 6'1", and he is the shortest, sibling in his family. The others are all taller than him.
My kids are tall, for their ages.
My 4 year old son, always gets mistaken for being older too.
I don't care about that.
He is taller, than many 1st graders.
Your younger son, at 48" tall... well that is tall.
You can always ask your Ped, about it.
But I doubt that Pituitary Tumors, are common.
Growth... is a very complex thing.
There are Pediatric Endocrinologists, too, and it is a very complicated field.
You cannot do anything about making them taller or shorter.