Oh goodness, @anitasharma, you have a lot on your mind right now! It can’t be easy being so far from home, away from the support of family and friends with your husband’s medical crisis and taking care of your children. It does sound as though your husband is getting excellent medical care and advice.
We’ll wait for the confirmation of the BMT and then we can talk more about that. In the mean time, I’ll try to put your mind at rest about your son being the donor. Yes, he most likely would be given a GCSF medication to ‘push’ the production of more blood cells to be donated for your husband’s transplant. This medication, such as Neulasta,(there are others) is generally used for cancer patients who have undergone chemo to help replenish their neutrophils quickly to protect them from infection. Other patients who have low white blood counts also use this to treat that condition. Your husband may have had this after his chemo treatments.

I’ve had several injections of Neulasta myself and it worked effectively. The only short-lived side effect I had was bone pain but it was handled with daily doses of a common over the counter antihistamine called Claritin. (Taken daily for several days following the injection).

For your son, this isn’t a long term application. He will have only enough to stimulate the cells for the collection and should be a minimal risk for anything harmful for him. This is pretty routine for cell collection.
There is another option for donor cells…that being finding a donor on the international bone marrow registry. There are over 41 Million people globally on the registry. Your husband’s doctors can also utilize that source if your son isn’t a match or if you’re concerned for your son’s safety. However, strangers are doing this for people they’ve never met, in increasing numbers. If it were too dangerous I don’t think they would go through with it. I’m grateful every day for my (then) 20 year old male donor (that was 6 years ago).

We’ll hope for the best with the biopsy in 3 weeks. Not everyone with ALL requires a transplant. But if your husband does, they can be absolute life savers.
Do you have a support system around you with family or is everyone back in India? Is there a possibility of your husband having his transplant back home in India where you’d have more support?