Quantine advice - 1 lonely existing fish

Hi all,
First, I'll start by admitting I made a big mistake, I had 5 lovely discuss in a 50gallon, but had added the most recent from a shop I hadn't bought from before. I quarantined him for 4 weeks and he appeared fine, so in he went. Now I have 1 lonely discus in my 50gallon (not him).
I want to step up my game and have learned a lot, so I set up a 130gallon. It's been running over a month, has some albino BN plecos, corys and black neon tetras.
I want to add 12 young adult discus and have a nice show tank, but I feel awful for my lonely discus.
What should I do as far as quarantining, should I even try to mix stock? NOTE: I am in Canada, so any suggestions of "oh just throw a thousand medicines at them" isn't helpful nor appreciated, we can't get that without prescriptions from a vet.
Option 1: move original discus to display tank now. Put new discus in original tank, quarantine and get them happy, healthy and eating. Move 1 new discus to display tank, observe. Move all discus to display tank.
Option 2: quarantine new discus separately, get them happy healthy and eating. Move all but 1 to display tank. Move 1 to original tank with lonely discus, observe.
Option 3: (less preferred) Try to rehome original discus. Quarantine new discus properly and hope lonely discus has a good home somewhere else.
Thoughts and advice appreciated, the new fishies are still 3-4 weeks away (Stendker from Discus Paradise Montreal).
Thanks,

I hope you buy the rest of your Discus from a trusted sponsor or from Hans. When you get the new batch put them in the 130. Wait 3 weeks to make sure they're doing well. If they are will, move your least favorite of the new fish in with the fish in QT. Wait another 3 weeks and if your neither fish gets sick from the other they are good to mix together.

Not sure how many sponsors ship to Canada. If you can get it have rid-ich plus on hand and salt. How big will the new ones be? How big is the surviver?

Thanks Liz and Iminit.
Yeah, that makes sense, not much point in an extra step for the new discus, I'll put them in the show tank. I know the tank is doing well as my plecos just spawned - happy about that, got the eggs out and will be able to raise and sell the fry.
I believe Discus Paradise are reputable sellers for Hans. I've ordered discus in the 2.5" size. My lonely discus is 4" or so. She is definitely stunted, I've had her almost 2 years and bought her juvenile. She's been through hell with hospital tanks and medication.
I have Nox-ich and Fenbendizole on hand - I know it's more awkward than other de-wormers, but in Canada we're limited in what we can get without prescription.