I know that majority of members may say to use the straight meat baby food mixed with some veggies, but I found that the chicken and vegetable baby food (stage 1)is much easier to swallow than the straight meat mixed with veggies...it's a texture thing. If that makes sense....just to get them started. I am pretty sure that it's perfectly fine to use the chicken and veg. This is what I used to get the boys going on food an it's still their favorite 5 years later.
You may only be able to get them to take a lick, but that's okay because every lick will help make them stronger and entice their appetite. Give them a lick 20 times a day if that's what it takes. Right now the most important thing is for them to get some nutrition no matter how little it is and to work on making a poop. Once they poop it will give you relief because then you will at least know that their little system(s) are working.
Wishing you and the little ones a great day!