I can see only one thing that can make it acceptable. First, Al Sev has to be Sorted Slytherin. Second, some time during his first year, Al Sev pulls some truly devious and humiliating prank (probably involving potions) on his arrogant older brother, James Sirius. Third, Slytherin House is so impressed, they declare he should no longer be known by the insipid name of Albus, but shall be known to all Slytherins everywhere as Severus Snape Potter. Fourth, Harry's head explodes the first time he hears his younger son's housemates call him "Sev."
Your art of these two is pretty amazing but to me personally, it's a little creepy (also considering the age differences and the fact they hate each other's guts in canon so having their names sandwiched together is an automatic fail). But whenever you do it it's an exception. I can excuse it.
Oh I'm not much of a Snarry fan and don't ship them. I ship Snack which most people find an odd ship, which is why I have no room to talk. Like you, the 20 year age difference bothers me.