Upvote:1
From a Theravada Buddhist perspective you're cats have already been reborn another place - impossible to say where unless one is a Buddha.
Try to be mindful of the wanting for them to be reborn in Heaven - the wanting/craving is what can/will cause suffering for you. You're cats own Kamma decides where they get reborn. You did your best to take care of them and love them. Be happy about that and take good care of yourself and your mind.
You can share the merits you've earned from performing The 10 Meritorious Deeds (one of them is meditation practice). You could choose to share the merits with all beings in the universe and by doing that your cats will recieve it too.