Actually I already made a post on this topics I am just copying and pasting my pov
shomi's situation is not a big deal at all
I mean situation like these exists so commonly in almost every Indian family
Now my Nani has 5 kids, the youngest among them is sonu mama, and the eldest is my maasi. So the difference between my maasi's daughter (my cousin) and my sonu mama is just 5 yrs. They practically grew together my cousin calls him just sonu. I thinks kids born in 90s would understand this, the difference between me and my mama is also only 10yrs.
Actually women can get pregnant until and unless they have menopause and some women get their menopause after 60 or 65
I think in like 80s having 5 to 6 kids was common, my Nani had 5 kids, and my dadi had 7. So actually my bua's(my father's sis/Daadi's daughter) son is just 3-4 younger than my chacha(my father's brother /Daadi's son). So my Bua's brother was almost of her son's age. So the same situation would be of swaragini.
So it's not about scientific situation, socially too this situation commonly exists in Indian households.