Damn, your Harry has a lot of growing up to do still (and growing a brain but that's admittedly even more unlikely ^_^)! Which means he sounds very much like in canon, so this is a compliment. I wouldn't have minded if portrait!Snape had been a bit less patient, forthcoming or forgiving towards Harry (and AD) but it made for a nice, conciliatory ending.
And I fear for Severus' children still at Hogwarts given Harry's attitude towards placement in Slytherin in the epilogue. "Well, theoretically it's okay to be sorted in Slytherin even if you're likely to be mocked and bullied by family members just for the possibility (And why isn't he putting a lid on that when he's clearly aware it's happening?! Making it clear that harassing of siblings based on House-afflictions is not tolerated in his family.), but know what? You don't have to be! Just tell the hat "no", it puts you somewhere safe and the problem is solved!" Yeah, right. That's progress >_<
Uhm, now that he's a magical picture I hope portrait!Severus gets relocated to his own home or at least an empty frame to "walk in" in his house! I guess he'd like to watch (over) his family much more than hanging around at Minerva's office all the time. And we know from Phineas that portraits can go other places so it shouldn't be a problem....
One thing - not just in your fic - though puzzles me completely. Among the tons of Snape-centered fics I've read over the years: whenever there happens to be religion involved, whether he actually believes, just grew up in a Christian faith culturally as most of us North and Western Europeans do (the UK being very secular in modern times!) or has parts of family being religious it's always, always Catholicism! WHY?
I've never seen him portrayed as a (true or nominal) member of another church. Not once.
Which boggles my mind, seeing that the dominant Christian church in the UK by far is of course the Church of England with 35%, having baptized half the population of England. If Snape was Scottish he'd most likely be a member of the Church of Scotland, their national church, and the largest religious group with 42 percent of the population. Whereas the Catholics in Britain are no more than 9 percent of the population... The Catholic attendance at mass on a typical Sunday in the whole UK lies around one million, so only 1 out of 60 Brits goes to Catholic church outside the "big events" Christmas, Easter etc.: much less than the Catholic percentage of population too.
Why this fascination with making Snape Catholic when he's four times more likely to be Anglican than Catholic?