Axolotl not eating? :(

Hi! So I'm new, so hopefully I'm doing this properly! So yesterday I rescued two three year old axolotls from an abusive home where they were rarely being fed and kept in a discusting small tank and they are both very thin! I have never had axolotls before, so this is new for me, but I do have a smallish aquarium fish so know all about water changes and introduction. Lotti (my little girl) is thin but she seems to be eating okay. I've been feeding her spiders, moths, axolotl food (from pet shop) and tuna. But my big boy axolotl Kingsley (hence my username KingLotti) has only eaten one cube of store bought food, I've offered him the tuna and spiders but he's not interested, not even in the store bought food! You can see his ribs I think? I presume that's what it is. So I'm just worried about him, is it just for the first few days while he gets used to his new home? Sorry this question has been so long, I'm just really worried about him!

What do you think about the names by the way? (Kingsley and Lotti)