I'm happy to learn from someone that they have the possibility to return home to their family they haven't seen for so long. Should I say "I'm glad (that) you return to your family!" or " I'm glad (that) you're returning home to your family!" Is "that" necessary? Is "return home to your family" said?
I would use a phrase that refers to a future or ongoing action: will be going, are going to go, or are going. There are many ways to express this idea.
As a complete sentence: "I am glad that you are going home to see your family."
You don't absolutely need to include "that," but it doesn't hurt. A way to decide: could it be confusing or strange without it?
"I know Monday is a busy day for you."
That could sound strange because "know Monday" might sound like you know a person named "Monday."
"I know that Monday is a busy day for you." makes the meaning clearer.
A dictionary will tell you that "glad" means "feeling pleasure or happiness". However, the way you use this (or any similar word) and the context in which you do so can have different inferences.
If you say to someone "I'm happy you are going" without any other context, that sounds quite rude - like you did not want them to be around and their departure is making you happy. However, if someone had just shared with you happy news that they were going somewhere they always wanted to go, the same words could sound perfectly sincere.
One way to express what you want to say sincerely and naturally would be:
I'm glad you have this opportunity to see your family!
This makes it very clear that your source of gladness is their opportunity to see their family and not the fact they are leaving.