Forgive my seemingly idiotic question, but do I purchase the half fare card on the SBB site first and then use it to purchase the Berner Oberland pass on the BO website? Thank you.
You do not "use" the HFC to purchase anything. You do not need the HFC in order to buy tickets at half price. Just indicate, during the purchase that you want a ticket with HFC reduction.
So you can even buy a BO pass with HFC reduction first, and then buy the HFC later. Or you can buy half priced tickets first and the HFC later. That you have the HFC is not verified during ticket purchase.
It is when travelling that the HFC will be checked. If you present a ticket to the conductor that has the half price discount applied to it the conductor will also want to see your HFC (and possibly also your passport...)
And it is perfectly fine to wait till you are here in the country with buying those passes. They do not need to be bought in advance. So if you are having issues navigating the websites, just do it all when you are here.
THANK YOU for your kind and thorough reply. I appreciate you!