As twin names go, they are just fine. Same level of spunkiness, same level of unusualness, without being matchy-matchy. So two thumbs up there.
As for the individual names, I never new Rosette was a people name. I just think of the riding ribbons. I'm not digging it. Second thing that comes to mind is Rosetta Stone.
I MUCH prefer Rosalie Seraphina.
I love both Tobias and Tobiah, but in your case I'd stay away from another -iah ending unless you want to be stuck in a theme. Two is a coincidence and three is a theme, IMO. If I had a fourth boy, I'd feel like I had to use another -iah name. I'd hate feeling trapped like that.
SO Tobias Malachi & Rosalie Seraphina GMV.
LOVE the middle names.
http://www.behindthename.com/pnl/56287