[RPG] the disadvantage of casting Raise Dead and then Restoration twice instead of casting True Resurrection

They can, with a catch and a few assumptions.

The only way RAW I could find to resurrect the victims using the Resurrection spell is by first casting Greater Restoration in order to remove the effect of the vampire's bite (since the victims are not vampires yet), and then cast Resurrection. The Resurrection spell on its own would fail, since the bite is still in effect. This would need to be done within 10 days, as otherwise the effects of Gentle Repose would go away and the victims would rise as free-willed vampire spawn.

This however, assumes that the vampire's bite, or at least it's health reduction component is a magical curse, that Greater Restoration can be cast on a corpse that is soon to rise as an undead without intervention (on the same principles that sleeping creatures are nevertheless creatures, even though the victims in the case would be temporary corpses if left unattended), and that Greater Restoration covers vampirism (assumption made from lycanthropy being able to be cured by Greater Restoration).

So, you fought some Vampire Spawn, which have the annoying:

Energy Drain (Su): A creature hit by a vampire spawn's slam (or other natural weapon) gains one negative level. This ability only triggers once per round, regardless of the number of attacks a vampire spawn makes.

Those negative levels provided by the vampire spawn are temporary until after the duration specified and saving throw mechanics. After 24 hours, and after a failed save, they would then become permanent.

Negative levels remain until 24 hours have passed or until they are removed with a spell such as restoration. If a negative level is not removed before 24 hours have passed, the affected creature must attempt a Fortitude save (DC 10 + 1/2 the draining creature’s racial HD + the draining creature’s Cha modifier; the exact DC is given in the creature’s descriptive text). On a success, the negative level goes away with no harm to the creature. On a failure, the negative level becomes permanent. A separate saving throw is required for each negative level.

What does this mean? The character is dead. The temporary negative level remains. The negative level would have to be removed, otherwise he'd just die again.

Raising the character from the dead would have to have a restoration spell handy to remove the temporary negative levels, the same as if it were permanent negative levels.

The temporary negative levels have a 24 hour duration. That duration doesn't wipe itself off the table by character death. If that were the case, then undead with a create spawn ability would never be able to create spawn - as their energy drain attacks would simply go away when the character died.

The only rule supporting spell effects that end upon death, without special text stating otherwise, is a spell effect that require concentration. Obviously, a spell caster can't concentrate when he's dead.

1. If the GM considers a dead¹ creature, as still a creature, cast Restoration on the dead creature. There's a little bit of precedence to back that up. Raise Dead, for example, says, Target: Dead Creature. Of course, Restoration obviously doesn't have the word dead in front of Target: Creature Touched, but, ask the GM to work with you a little. The worst he can do is say no.
2. If you don't have a Restoration spell handy, raise the dead character back to life, and the proceeding round cast Death Ward. That would make the character immune to the negative effects of the negative levels for the duration of the spell. That could afford you more time, especially with multiple castings of Death Ward.
3. Raise him from the dead at exactly 24 hours from his death. That would give the party time to rest, have that much more preparation time (i.e. hireling services from a cleric, purchases of scrolls, pray for spells, etc.) and allow the newly raised character, with the negative levels, a quick chance at a fortitude save.
4. Wait for the negative levels to expire and become permanent, and proceed to raise and restore as the rules are explicitly clearer on - probably with the assistance of higher level spell caster NPC's in a temple at the next town.
5. Make a new character.

¹_{Being dead doesn't say you become an object. It just says you are a dead character. It also doesn't say effects end when you're dead. It does say, if you are raised, you're raised in the same condition as when you died. If you have temporary negative levels when you died, and are then quickly raised, you'd still have the temporary negative levels.}