just make the levels they learn pyoak's moves higher.
Say for pyroak.jr hyper beam at level 80, and pyroak.jr.jr level 85. or just don't give them it.
That's not how it works. Pre-evo's learn moves earlier
. Say, by 5 levels. Or not at all. Hyper Beam is just the wrong example, because that move is only learned by a few unevolved Pokemon (Dragonair, for example), and for the rest exclusive to fully evolved ones.