UPDATED Baby's with leg braces?!

This is NOT for my own child. I am a infant room teacher and today I had a happy, 26 pound baby start. He's 11 months old and the youngest of three. Mom didn't say much and I tried asking questions but she was Nervous.

I noticed through the morning that he does not crawl. He does not stand well even while supported. Our director later came in and told us he had a genetic? Disorder (his siblings had it as well) that he has braces on his legs when he was much smaller and now they are off.

So I'm looking for ANY adivce on how to help him gain strength in his legs without hurting him. I will ask mom the same at pick up. I just hate that all he does is sit all day watching my other babies crawl around.

UPDATE:

Dad says that he (dad) was the one with braces and needed them for some unknown reason. The other kids DID have the problem but did NOT need braces. However they are still not concerned about him not being mobile, even though this baby has the same symptoms as dad did when he was little. They're just trying to get him to walk but he can't even stand.

I know it isn't my place but I just want to get this baby moving! Is he maybe too heavy, 26lb 11 month old remember? I tried him in a jumperoo and he hated standing after 10 minutes. He's totally content laying or sitting on the floor or just cuddling. Also he's still only drinking bottles and is slowly adjusting to table foods. I just want to catch him up, especially because mom is pregnant and due in June, and can't even hold this little man because he's so big😟😦