Monster reborn question

Okay, here’s the fight I’m trying to mediate. Red eyes zombie necro dragon was properly summoned into the board. It was sent to graveyard in battle with a five headed dragon.

The five headed dragon player than played monster reborn. I believe this would work in the necro dragon because it was properly summoned. However, I feel that the necro dragon cannot be put into play because the player already has the five headed dragon in his extra monster zone.

Please help, my kids are going to kill each other.