Okay so I remember this moving playing on Disney channel when I was a kid.
It has 2 kids, a boy and a girl. They are orphans I believe and twins I think. They get adopted by this man or woman but the person is rich and trying to buy everything to make them happy but they’re not. There’s this mountain that glows green and they’re attracted to it for some reason. I believe the person buys them a pony. I know the details are scattered I’m sorry.
I am going with (yes …) the “made for TV version” of:
Escape to Witch Mountain (1995) – https://www.imdb.com/title/tt0112985/
– It has 2 kids, a boy and a girl. – Check!
– Orphans – Check!
– Adopted by a rich (a “magnate” even) guy – Check!
– There is a horse involved. – Check!
– Attracted to a mountain. – Check!