Planetary War and the effects on the house Lord
For any developmental issues start with the Moon and then examine mercury as well. ALso, be aware, there may not be any developmental issues but the child may just be on a different track and so be misunderstood.
I see, sorry to hear that. For genetic disorders always examine venus and the first house. Venus is the genes and the first house is what we are born with.
Twins show us how sloppy of astrologers we are and that anything concrete we get correct from the Rasi is due to luck and intuition. Astrologically, its about ALL the vargas. Check which vargas are there and how certain planets will move from good to bad bhavas and you will find the explanation there.