Re: I’m shocked
LOL…this is like planning the honeymoon when the engagement hasn’t even taken place. 
You’re getting WAAAAY ahead of everything with this custody assumption.
I’m sure the girl’s mother is fully capable of looking out for her son’s best interest. First find out if your’s friend’s familiy is even willing to consider a widow with a son. After than, you need to find out if the girl has any interest in marrying again…and if so then if she’s ready to consider rishtas now.
Unless you know the girl’s in-laws personally and know for a FACT that they will try to fight for custody if she re-marries…then you can bring this up. But otherwise, it’s not even an issue at this point.