Activity for Vivian

So my mother has just two siblings, and her only brother has a substance abuse problem that has left him off even his own daughter's wedding guest list. My father, who isn't even blood related to this man, has convinced me inviting him is the right...

I am hand lettering the addresses on my invitation envelopes. My invitations are pretty formal themselves, and I am using formal titles on the envelopes. I'm wondering, what would be the proper way to address the envelope to my father and his fourth...