@Baraf I found your post really interesting if you don't mind i'd like to ask how practicing in deen were the parents of the individuals you spoke of? If the kids turned out to be anti Islam and anti culture were their parents more laid back moderate muslims?
There's two types of people who marry out. The non deen practicing somali man or woman who doesn't really care much for culture. When this type of a person has children they will obviously not teach their kids Islam. They will raise their kids like gaalo kids, do whatever you want, come in when you feel like it be gay/straight etc and instill a hate for their culture in them.
Then there is the the well cultured good muslim Somali who marries another good foreign Muslim. This kind of couple will take their kids to dugsi teach them about Islam and culture. They won't alienate their kids from the families, community so they grow up to be proud Somali kids. I grew up with people like this and they all speak fluent Somali and have deen. So it depends on the type parents and the environment where these kids are raised.
If the father isn't Somali, the children aren't Somali.