The world isn't really overpopulated. There is enough food to go around easily. It's distribution of food that it the real problem. You could fit the entire population of the world, standing side by side, in the city of Jacksonville, FL.
At best you can say, sections of the world, like Tokyo, Mumbai and Shanghai are overpopulated, but Japan, India and China all have areas where it's underpopulated.
You have to remember she is giving birth one at a time and each of those kids is also helping to raise their siblings in a way. So the mother can give proper attention to the little ones. Because as the kids age, the older ones need less attention. You could make a reasonable argument that siblings helping to raise their siblings isn't fair, but I don't see it as a crime.
I had two brothers and a sister, and when I was 5 my brother was 15. I can see how sharing a bedroom with me, at age 5, would be hard on a teen aged 15 year old, but it's no real big deal.
I'm not saying there aren't issues, the whole situation could be whacked but I don't think you can say it's off simply because of numbers. Yes, the more kids, the more problems, but the likelihood of an issue, doesn't mean the issue must exist. The same way I'd say, two parents is the best situation. But one parent (male or female) can do an equally good job. It's just not ideal and they'll have to put in more effort
As for late life babies, the issue is more about first babies than anything else. You find birth problems in women over 40 that have never given birth. If a woman has had babies before 40 and especially 35, the rate of problems over 40 drops. My own mother gave birth to me at 45 and the previous time she was 35. She said, my birth was the easiest time she had and one of the easiest she had seen. She was a nurse in pediatrics so was present at a lot of births.
I'm not saying any of you are wrong, you could be right. I'm just saying, you really have to judge each case individually. This woman may very well have problems and the kids may be in trouble. Or not, I'm just saying size alone can't be the factor