we have a 25 YO, a 17 YO and an 11 YO...
The 17 YO didn't always live with us as he is my Step son but we decided a long time ago that since we are a family ,we did away with the word step.
When they were younger it was hard. A LOT of only child stuff going on.
But now things are nice.
The 11 YO can't wait for her sister & Brother in law to have kids so she can be an aunt.
The 17 YO helps his sister with her homework and teaches her how to stand up for herself and some "cool" teenage stuff..
They are both into anime and a few other things like Disney

He is very protective of her - of course he knows everything and is always right
The hardest on me is doing the teen years over again 3 times

there seemed to be way too much drama from the 25 YO when she was a teen,
the 17 YO is "Mr. I know everything and I am smarter than you" and
the 11 YO is going thru her tween stage.
Things did work out and it has been fun!