If i sell a ranked monster will the ranks still count in the library? Cuz some are easy to rank and some take time. But due to this confusion im running out of space. So if they still count then ill gladly sell them.

If you rank-up a monster, then they should show up ranked in Monstagram (and stay there if you sell them).
However I don't what happens with book pages.
I always extract the ones I can't breed and sell the ones I can (even if it takes more time).

They stay in monstergram and library books. If they didn't then it would be a nice bug as I would constantly breed one monster for all the rewards then kill it and repeat.

@ibobs72 good point