Teutonic Knights are HRE only.

England can get Templars and Hospitalers.

Spain and Portugal Knights of Santiago.

Dunno about the other catholic factions.

They all have attack: 13 defense: 16 charge: 8 and some skills like stamina, moral etc.

You can see which faction can recruit which knight order in the unit rooster of custom battles.

Btw the chapter houses are all the same, exept the biggest hospitalers which have the additional benefit of +15% to health.