An arms race over a familiar's species designation? I'm sorry, but that's the most ridiculous thing I've ever heard. Just kill the damn Owl. Flyby + Help action leaves it a maximum distance away of 60ft, which is well within range of most attack Cantrips and all non-Hand Crossbow, non-Thrown ranged weapons. If the DM pulled a similar stunt with an enemy Wizard, any of the parties I'm in at the moment would kill that familiar within the first round of combat, and the DM should feel free to have the enemies do the same. The thing is, if you did that; if you sent a reskinned Owl against your players, do you think they would complain about how unfair that is? Do you think it would bother them in the slightest, or do you think they could deal with it pretty frickin easily?