Target creature gets +2/+2 until end of turn.
Equipped creatures you control gain indestructible until end of turn. (Damage and effects that say "destroy" don't destroy them.)
If the target creature is no longer a legal target as Resistance Reunited tries to resolve, it won't resolve and no creatures will gain indestructible.
The set of creatures that gains indestructible is determined as Resistance Reunited resolves. After that point, an equipped creature that gained indestructible won't lose indestructible if it becomes unequipped. Similarly, one that didn't gain indestructible won't gain it should it become equipped.