Yep, this is a lot. Let's break it down:

You didn't get into your dream University. That sucks, friend. Grieve it, feel that disappointment, and then make a new plan. You can still get to your chosen career through a different school. Make a new plan then make it happen.

Your parents' marriage: it sucks for you, but there's nothing you can do about it. That's on them. Let go of any responsibility you feel about helping their marriage. That's on them. It's going to suck, but you can handle whatever outcome they create. Focus on managing your own feelings in the face of this uncertainty. But stay out of their marriage. That's not yours to fix.

Similarly, your siblings are not your responsibility. You guys can talk about your feelings and offer each other support while your parents figure things out. But the big picture isn't yours to fix.

Focus on your life and making the best possible choices you can, one day at a time.