Any recommendations on how to care for ducks that came from a hoarding situation?

I (19F) and my ex (20M) have recently started talking again after he and his girlfriend broke up. While they were together, they had 18 guinea pigs and 2 ducks. Since they split, she basically left all of the animals behind. My ex is a truck driver, so he’s gone for long periods at a time, and it honestly seems like neither of them wanted the responsibility.
From what I know, the guinea pigs weren’t being cared for properly. I don’t think they were even getting fresh vegetables, and there were times they were fed only hay for days without pellets. They all lived together in a tiny studio apartment with barely a proper kitchen, so I genuinely don’t understand how they thought they could properly house that many animals.
They’ve been broken up for a couple of months now. She recently came back, trashed the apartment, took the guinea pigs, and left the two baby ducks—who are only about 3–4 months old—alone in the filthy apartment. She completely abandoned them.
After a lot of convincing, my ex agreed to let me see one of the ducks. He wouldn’t let me inside the apartment and only brought one out because he said the other one was “too dirty.” That immediately concerned me. I asked if they at least had a kiddie pool or somewhere to bathe, and he told me no. I was honestly shocked. After I said something, he claimed he was going to buy one.
He also admitted that he doesn’t even want the ducks. I told him that whether he wants them or not, they’re still his responsibility, and not wanting them isn’t an excuse to neglect them.
When he brought the duck out, my heart broke. This baby looked so skinny. I’m a veterinary technician, but I’ve only worked with cats and dogs, so I’m not very experienced with waterfowl. I do, however, have four parrots—two green-cheek conures, a sun conure, and an Indian ringneck—and they are my entire world. Meeting this little duck made me fall in love instantly. It was so sweet, and I wanted nothing more than to bring it home, but unfortunately I already have a full house of pets, all of whom are well cared for.
He said he doesn’t have much time for them. I even offered to stop by every day just to bring them proper food and vegetables, but he refused because he doesn’t want me in his home. Honestly, I think he’s embarrassed by the condition it’s in, but I couldn’t care less—I just want the ducks to be okay.
I also offered to schedule them for a wellness exam at the avian clinic I take my birds to. I get a discount there, so it wouldn’t even be that expensive. He claimed he’d already taken them to a vet before, but when I asked which clinic it was or if he had the records, he got very vague. I honestly don’t believe him. I even offered to take the ducks myself, pay for the visit up front, send him the receipt, and let him reimburse me later. He still refused.
He said they have “pellets the vet recommended,” but again, he wouldn’t even tell me what brand or where he got them. When I asked if they at least had fresh drinking water, he told me he had just gotten home and had only given them water moments before I arrived.
I feel absolutely heartbroken for these ducks. They deserve so much better than this. I’m frustrated, disgusted, and honestly don’t even want to continue speaking to him after seeing how little concern he seems to have for them.
Has anyone dealt with ducks coming from neglect or a hoarding situation? Is there anything else I can do to help them or encourage him to either properly care for them or surrender them to someone who will? I just want these babies to have the happy, healthy life they deserve.