In order to disown someone, you must be first in a position of ownership, meaning having authority over them in terms of their relationship to you. If such is the case, you may indeed disown them. If, however, you have no positional authority, then disowning them is nonsensical. It's like firing a person who is not in your employ!
Just because you can disown a family member doesn't mean you should do so. Example, I can technically disown my nephews who were baptized Catholics and now, as young adults, live as if God doesn't exist, in a state of complete indifferentism. Since they were raised by a religiously ignorant Catholic mother and a "not-religious" Protestant, it is unwise to "disown" them. If they are to hear the Truth from any family member, it will be from me. Maybe your situation is different. Perhaps your relatives' behavior is blasphemous or seriously scandalous. Then it may be your duty to disown them.
When it comes to family or associates over whom you lack authority, you may choose to distance yourself, cut off all contact forever, or anything in between. What effect does the apostasy have upon you and upon those in your charge? Do you have an obligation to the apostates? Example, your elderly parents have denounced the Faith. If they are in need of physical sustenance, as their child, you may not disown them. You lack authority over them, and you're obligated by honor and charity to provide for them.
As for "disowning" colleagues, employers, dealings with non-Catholics, good luck to you! I hope you can be totally self-sufficient by yourself without any but homemade supplies, food, services, etc.
We are in the world, but of it.