Rubbing their bellies harder won't help. You could try warm compresses, that can help. They aren't defecating properly and probably have a lot of fecal matter that needs to pass. Gas can be an issue, but being impacted badly is usually deadly. Newborn kits are at serious risk for this when being handfed. I wish you could find a local breeder to help you out at this point....someone with some know how would be best. I'm not sure if a vet could even help you.
(This is one of the reasons why I tell people to please, please not start breeding chins. It is heartbreaking to lose the mom if she has an issue giving birth, but also completely devastating to lose kits that you have been handfeeding...)