Scholars travel passes

I'm trying to figure out the best way to get scholar travel passes for my son in previous years he has used a buzzy pass locally on De Lijn because we are outside BXL communes.
He also has A Mobib I imagine STIB but not sure which we took last year.
This year it would be better he sometime takes a train from La Hulpe and also has a Mobib and buzzy pass but I'm struggling to understand all the websites or how to combine the train and metro pass. Would a MTB school pass work on trains as far as la Hulpe do I need to get him something else? It's not easy to find out what the difference is between MTB and STIBThey seem to think you know the difference I understand it's the area you can go but once out side of BXL would I need something else entirely I presuming being Belgium going to be yes but asking in hope someone can offer advice