Stacking Hero blessing?

well, only if i had a legendary ephraim right now, i could figure. also, conferring blessings? it just replaces the one that's already there

If you mean getting boosting more than once by legendary heroes, yes it is possible with L!Ike and L!Robin. The other 2 non-legendary units will get a massive boost of +6 HP, +2 Atk, and +3 Spd.