The paralogues for the children of azura, your avatar, kaze and silas are all easy as hell regardless of difficulty setting or where you are chapter wise in each campaign. If you don't have them unlocked yet you can always grind support levels safely in my castle battles and then do them to level up the members who are lagging behind.
That said remember that exp is precious and limited in conquest ( unless you buy the exp dlc) so you want to be making sure the units you are putting effort into are the ones you want in your main team come endgame.
Also remember that it's much easier to equip a lowish might weapon, preferably with no crit ( to prevent accidental kills) on your tanky characters. You let them take a beating during the enemy phase then switch and clean up the kill with your weaker characters on the next player phase.
