Elder McNamara and Harding both keep saying they are too busy to talk. I gave the holotapes to Harding and right after that it said I completed the quest, and they have been like this since, even after leaving Hidden Valley and coming back after a few days. I'm assuming this isn't normal?

From the Fallout Wiki:

After fixing the air filtration system, and then helping Hardin oust McNamara, you will not be able to speak to either of them forever. Hardin will keep saying he will have his hands full for a few days, and McNamara will keep on saying he must prepare a defense, but no matter how long you wait they will keep saying the same things.

Is this what you did?

I had the same problem. There's a glitch that allows the player to play this quest helping McNamara and Harding at the same time. Actually the game should allow the player to play only ONE of the two options.
If you decided to play both the ways, the game glitches and then you can't go further with the Brotherhood quests, doesn't matter if you wait or if you do something else after the quest end.
If you can, I suggest you to use an earlier save. Otherwise you must to restart your game, because there's only another way to obtain Power Armour Training (Arcade Gannon's quest), but it's a long and pretty difficult way.
Of course if you decide to start a new game, I suggest you to wait for the incoming patch.