I’m glad the two kittahs are doing better. Yes, you need to keep trying to get them poop. You can put a couple drops of olive oil or vegetable oil in their formula. This will make it easier for them to poop. Please read the link KZ provided as they have a lot of useful information.
This is from the messybeast.com link that KZ provided:
CONSTIPATION
This is fairly common in hand reared kittens. A mother cat stimulates a kitten’s anal region frequently. A human surrogate may only stimulate it two or three times a day. Kittens should be stimulated to pass a bowel motion after every 3 feeds otherwise faeces accumulates in the rectum and colon. The longer faeces remains in the colon, the more water is reabsorbed from it and the drier and harder it becomes. This in turn makes it harder to expel the motion. I’m angry at the vet. for so dismissive of you needs. However, you should call and find a vet. who can help you for a reasonable price. Contact the shelter for advice or references on low costs assistance.
Here is a link to help you find a vet. near you that can help.
http://www.humanesociety.org/animals/resources/tips/trouble_affording_pet.html?credit=web_id91754962#Assistance_by_state