Thank you for your query.
Though you have mentioned that your twin girls had a lot of digestive problems in the beginning you have not specified what the problems were. I presume that they were having frequent diarrhoea
and have been diagnosed to be allergic to cow milk and there is no problem with the soya milk being given to them.
Enfasoy Formula no. 2 is recommended to be started from 6 months onwards. However there is no hard and fast rule about it. It can even be started now. You need to work with their actual age (chronological) and not calculated age.
Though it is recommended to exclusively breast feed the baby till 6 months of age and introduce weaning food thereafter. In my practice I start liquid diet
from 4 months of age and gradually shifting to semi-solid and solid diet by 6-7 months of age. As your twins are being top fed you can gradually start introducing liquid diet in the form of soups, fruit juices, etc. I will reiterate that there is nothing hard and fast when solid diet be introduced and it can vary according to local traditions.
I hope I have answered your query to your satisfaction.
Wishing your twins all the best.