While she has those stoneskins, she will take 0 damage from all sources. However, if you kill Suparna first, then Garuda no longer has them, even though Chirada is still alive. This means that you can melee LB Garuda once Suparna goes down; you can caster LB both Chirada and Garuda so long as the spiny isn't nearby.

Alternatively, you can choose to LB Suparna or Chirada with a melee LB. Don't try to caster LB both Suparna and Chirada.