I feel like she should have taken the title and like in the future when she have kids the ...

THATS WHAT I WAS THINKING

YA RIGHT! SINCE THEY HAVE SO MUCH ISSUE ABOUT 2ND CHILD CAN HAVE THE TITLE

That's not how it works. You can't forfeit your title and then years later give it to your child. When you forfeit the title it goes to someone else.

Besides that, if there is no one to carry on the title; the title, their family name, their feif, their wealth and etc. die out and gets taken over by the ruling royalty.

That too

Succession for heirship and titles is a literal one and done. There is no second chances, no "I will rethink this later", no "Damn. I want my title back" years later. Once the papers for disqualification and for renouncing your right to the title to are given to the proper authorities and then later, the ruling royalty, there is no going back. The only way someone has a chance second chance at a title they renounced is if and only if, there are fears that line will die out and if your bloodline is beneficial to the kingdom, the ruling royalty will give a second chance to a renouncer. But that's means everyone else in line for that title has to be either dead, not fit for the title, or disqualified. For that to scenario to happen is very rare.

I was thinking maybe he could return it to his father or smth idk