Advice regarding kittens being born at different stages of development.

Hi, I have a beautiful Hymalayan cat and after a long search for a male she would accept she became pregnant. I was there during mating and it happened four times within 24 hour period and then I took him back to his house. The pregnancy went smoothly, kittens were moving and out of nowhere I discovered still born kitten on the living room floor six days before her due date. It was at three o'clock in the morning so I turned the lights on to find momma cat and discovered another baby on the floor still in the sack and the placenta attached. The first one was only 47grams and totally hairless, but the other one was fully developed weighing 65 grams with hair all over his body. I was devastated, but in the morning I felt more movement in the belly so I was like a hawk watching over her making sure she wouldn't hide anywhere. She was completely comfortable, eating and drinking as before. She didn't seem to care about the babies as she probably had no idea what they were as this was her first pregnancy. Two days later she meowed her head off forcing me to sit on the couch next to her and five minutes later her contractions started and a live kitten was born ten minutes later, another one followed in thirty minutes. Both were only 58 grams with no hair on their feet belly and most of their heads were also pink. They were so tiny so I had to help them every hour to find and stay on the nipple which was about 20 times harder than having a newborn human baby. The mother took really good care of them, but still one day later one stopped eating so I tried to give her formula and it got terrible colic and didn't get out of it. It was so painful to watch her suffer. The other baby took three days to finally start gaining weight. She is now ten days old and weighs 135grams. So the question here is if any one of you might know of any reasons why the kittens were so far appart in development while inside. I would love her to have more kittens in the future, but if it's something that is likely to happen again, I wouldn't risk it.
Thank you all ahead of time.

Yes. This is probably not that unique.  Usually the explanation is easy and given by itself:  she mated several times during a too long time span. Or even by different males during a long time.   And thus we do see here the result... So even if they may counterbalance this with pauses in the delivery,  giving birth at roughly the right time to each one - even a couple of days apart - still such things do happen...

Which in your case, with a totally controlled situation and monitored mating, we got the proof its fully possible to get start together, but landing totally separated. So to speak.

So you and your girl, and her babies, gave us an unique insight.

But my comments and insights back?   I really dunno.

I could guess on some genetical combinations - from her or from the male, but I really dont know.  The only I can get at this moment, one of our forumists swore her persian did delivered each time on day 58, no complications.   I suppose she belonged to a line of early deliverers, but day 58 is the extreme of what is biologically possible.

That said, maybe is that so there are persians strains whom do deliver earlier than the average.

Anyways, Im happy at least one did make it so far, and should proceed now smoothly, if God so wants.

Ok, proceeding to what Im decently knowleable about; taking care about  viable prematures.   The two later borne, although very premature, were apparently fully viable - because what they usually die from, is too weak lung function, dying in minutes from the birth.  As even the weaker one survived several days, and died not from some lung problems, but from constipation.   And yes, severe constipation is serious, especielly in a weak kitten.

What kmr did you used?

What activity against constipation did you used and tried with?   @fluffy baby