I had this happen at the beginning of the year only mom came down with PRE eclampsia.
I raised a litter of 5 from birth and I used a home made formula and they gained like weeds
I also fed them every 2 hours 24/7. I personally think the 4 hour span is too long if they are new borns.
Its alot of hard work but I'd do it all over again if I had too. Mom was great and she wore a onsie and I fed the babies and she did the rest. We were a wonderful team