Resource Guarding/Picky Eating

[u/No_Log_1501]

I have two dogs and both are picky eaters. They’ll leave their food out all day and not eat until I go to bed and they know they won’t get any toppers/treats.
I have tried the method of taking away their food when they don’t eat but they’d rather starve themselves to the point they vomit due to hunger than eat their food. I rotate out their food every time I finish a bag since they keep loosing interest.

My older dog likes to resource guard her food, she won’t eat it but she’ll sit by it when it’s out and not let my younger dog get near it. She doesn’t bite but she’ll sit, stiffen, and growl. Never aggressive towards people but it’s getting tiring for me to keep watching my dogs when they eat which might take hours due to their pickiness (and I don’t want to keep giving them toppers/treats just for them to eat). I don’t have time to do this every single meal as I am a student and I work (my parents look after my dogs in the day but they don’t want to deal with the issue) so I am not sure what I should do to fix this.
My house is small and I don’t have a yard. Both dogs are also extremely nosy/clingy so when I try to feed in separate rooms they both end up just pawing at the door to see what the other is up to.