I don't know how to digest this information. I feel like I want to say I understand this happened but I "feel" like he was talking about someone else. It is just so surreal. He was so calm when he told me about this and me on the other hand can not stop crying.
There is no one way to digest the information. For him he has been trying that for a long time and it probably hasn't been easy for him. What is a little easier and more productive is to notice how the information is handled each time it comes up, as you are doing.
To which he responded that family is family, he still cares for all of the family members. How? How can he be so "normal" ? How can he still be so nice to them, to her? (He has a tendency to put other people before him)
You may not respond the way he does, because you have not had to deal with the experience in many different ways. Some of the ways he has dealt with it may have been helpful. For instance, he may have some perspective on why it happened and hasn't been able to share that fully, with himself or with another person.
His statement that "family is family" is true and he probably does care about them. Sometimes that caring is all that can be held on to amidst the confusion about what happened. Other feelings may be there, but it can take time for them to surface.
Your patience may help. Don't forget to ask for the help you need too.