I'm using Deadly Dragon Spells and it has a revive spell to bring dead NPCs back to life (obviously) what I'm wondering though is Lydia died and I received the *letter of inheritance" same happened with Faendal so the game must be registering them as dead, would bringing them back have any negative effects?

No that’s only if the dead body is near you and you cast the spell or shout on them. They will come back to life and fight on your side for a short time.
I don’t do it do to they turn to ash once they die or time runs out on them again. PS3 Skyrim does not have an ash clean up so the more ash piles accumulate the more memory they take up. It’s one of many problems with PS3 Skyrim.
If the character is dead and the body gone, it will not bring them back.
Even if the body is near you and you bring them back its only for a short time and I mean short MAX time would be about 1min 1/2.

I think you wandered into the wrong section, Lord Raven...

And AFAIK, there are no issues caused by resurrecting followers who were killed - story importants are another thing, but the inheritance note is pretty much a fire-and-forget on the game's part.

Lol I was wondering why I was so baffed on that first reply.

@AstralFire - OK thanks, was just a little concerned the mother ship might land in the middle of Whiterun later down the line if I resurrected anyone.

Sorry The first part of OP is: I'm using Deadly Dragon Spells and it has a revive spell to bring dead NPCs back to life (obviously) what I'm wondering though is Lydia died and I received the *letter of inheritance" same happened with Faendal so the game must be registering them as dead,
My Response was: that’s only if the dead body is near you and you cast the spell or shout on them. They will come back to life and fight on your side for a short time
The end of his OP was: would bringing them back have any negative effects?
I don’t do it do to they turn to ash once they die or time runs out on them again. PS3 Skyrim does not have an ash clean up so the more ash piles accumulate and use more memory. It’s one of many problems with PS3 Skyrim.
If the character is dead and the body gone, it will not bring them back.
Even if the body is near you and you bring them back its only for a short time and I mean short MAX time would be about 1min 1/2.

You missed the part where he's using a spell that's not available on the PS3, and has nothing to do with the raise undead spells. >_>

Well I dont mess with spells. Sorry.

The game will treat them as though they're dead, so if a dead NPC is involved in some role in a quest, that quest may not progress because of it. Not all quest important NPCs are unkillable beforehand.

Everyone who has a topic about someone being dead will say so, if they get a grave in one of the Halls of the Dead, that NPC may yet disappear at some point in your game to be replaced by that grave.

Assuming of course you resurrect them via the console that is. The "revive" spell is temporary and they're just zombies under you control.