This is so heartbreaking and they do grieve like humans do. I have no advice to ideas on what you could do other than to pay far more attention to them than ever.

Just a thought here and maybe it is a way out thought.. You took Pidge out of the house and she never came back.. Could they be afraid you will take them away and never bring them back?

I would contact Nancy and see if there is anything you or she can do to help. We never had any idea how bad Mama's death traumatized Boo until she told me that. Pidge being taken out and never brought back has surely traumatized them. Maybe they need to know YOU miss her too and are grieving just as bad as they are. Nancy said Boo just wanted to be heard and have her feelings known so we would understand HER feelings and that made all the difference in the world for me and for Boo. I think Nancy could help! It is worth a shot if it could help them and YOU! Maybe Pidge might even come through and talk to them and let them see she is alright now. I would do it in a heartbeat.