I find it hard to understand how close family members can have anything to do with a relative who's committed a horrific crime. If I was related to Vincent I wouldn't have anything to do with him ever again. But we're all different.
I think it would depend on what sort of relationship you had beforehand. I have never had any reason to not like or trust any of my close family. So if something as horrific as this was landed on my doorstep tomorrow, it would not stop me loving the relative.
I would be broken hearted, and I would stand by him/her.
However if the relative was known to be of bad character and had caused the family a lot disruption already, then my feelings for him/her would not be so strong anyway, and it would be easier to separate myself from him/her.
I feel sorry for the Tabak family. If they have had no reason to ever suspect anything unsavoury about their baby brother, it must be very hard for them to take.