So before I'd started bottle feeding them there had been 5 kittens (one had been found later on, so actually 6 kittens) starving from one of my cats, Babu being the supposed Moma cat's name. I was at my Mother's when the first two had died and (though I don't agree with how my brother did this) put in bags an placed away from the house. I come home to see three little starving crying kittens outside not being feed, cleaned or anything! I ask my brother and he says, "Babu isn't feeding them. Two are already dead." I freeze, give him a look of distraught/confusion, and ask, "You haven't messed with them, right?" He says something like, "Only when we were getting 'rid of' the dead one." though he didn't say it that sadistically. After like a day of prattling to myself, I ask my Dad if I can feed them cow's milk, (I didn't know it wasn't bad for them at the time. Even after I knew I didn't want them to die so I kept giving it to them and they'd seemed fine to me for the whole time.) he said yes so I started feeding them. Then, my brother found another kitten and I started feeding it. I even named them, those names being Steez (the black one), Snart (the small grey one), and Archer (bigger grey one and the last to be found.)! After a couple days, the black one started to consistently cry one day, not a "I'm hungry feed me" cry but a "I'm in pain." I tried to calm Steez by singing, petting, and talking to it, it finally fell asleep so I put it outside along with Snart and Archer. I read up and printed out a Vet form so he could go to the vet because it seemed he might have gotten some milk in his lungs. I go outside to check on them and the other cats an he's dead. The next one Snart dies, them being inside kitten because I thought Steez had had a heatstroke, when I convince my Dad to go to PetsSmart (even though we ended up going to PetCo) so I can by kitten milk. Only to walk inside ready to feed them and find out Snart died. I went down stairs, where my brother was watching Archer, and started to feed the last kitten the kitten milk. An today Archer hadn't wanted to drink milk and kept spiting some of it up, not at the level of Steez or Snart. I left him to sleep after he drank all he could, come back into my room (which was at the right temperature for a kitten) and see he's about to die, I spend Archer last minutes petting him. Me and my Dad go and bury Archer next to Snart and Steez. So I'm wanting to know if I was doing anything wrong, aside from the cow's milk, or if they just died because of a sickness or because they were Babu's first litter.
Just have a question before I write more, did the kittens poo at all and how old were they? It is very common for them to get constipated and die quickly, because the mother cat usually licks their tummy to massage it so that they poo.