JUST A SIMPLE GUESS: 😊
Our dear dadi2 must have had 2 sons sajjan and someperson. Sajjan had a wife who bore him krishna while the second son's wife must be amma who bore him shakti. Later maybe due to some reason sajju's wife and amma's hubby dies. Dadi 2 and husband get amma and sajju married thus resulting in komal.
This maybe the reason ss cares less for shakti and more for krishu and komal. While amma cares more for shakti and komal and less for krishu. Maybe amma may have brought up krishu from a very young age, as krishu's mom died in childbirth.
Shakti and komal are gone case just like their mom, while krishna doesnt show much of amma characteristics, he has a little goodness in him (from his biological mom) and some sajju's characteristics. Thus, krishna cant be amma's real son.
P.S.: can piyasa be komal's twin sis, kumbh ke mele me bichri hui.....she has all the heriditary features off amma.😆😆
Any other ideas....pls add