a player has a monster and activated return from the diff dimension and selectec 4 light monsters and special summon them,declared an attack,opponent uses mirror force,monster were sent to the graveyard..main phase 2,player activates 2 ray of hope and got the 4 light monsters that were special summoned earlier and add them to his deck..end phase..

will those monsters selected through ray of hope be removed from play?

No, monster brought back by RftDD, which are sent to the grave, deck or hand, are NOT removed again.

or even if they are flipped face down, they won't get removed.

The only time the returned monsters get re-removed is if they are still face-up on the field during the End Phase (with nothing else removing them from the field in any way or flipping face-down).