I would alternate - not try to do both.
Poultry Nutri Drench has some calories in it and a few vitamins.
I think there is a tube feeding link somewhere . . . wish I had a more photographic memory.
See if any of this helps
https://www.backyardchickens.com/t/805728/go-team-tube-feeding
I...
I would go ahead and put a teaspoon on their food once a day - small grit, that is.
The vitamins sound good. If she has an infection, she will need antibiotics - I am not an expert on type and dosage. That is where a vet would help. There are bits and pieces of information around, though...
While I would keep the water and food available for at least 8 weeks, I agree with the rest of what is in the first post here
https://www.backyardchickens.com/t/750869/raising-and-caring-for-ducklings#post_10611711
Do they have a way to clear their nares (nostrils)? You might try letting...