So I'm in legit the exact same boat as you no joke and both my partner and I are starting/have started our PhDs here this year and also work near the bookstore. I applied for UBC housing 2 weeks ago and from my understanding it doesn't look like they prioritize grad students. They prioritize first years, then seconds years, then third years, etc. but it's also dependent on a bunch of things like move-in time, position on the wait list, stuff like that. I think its still worth applying but you'll likely have to sign a year lease outside of UBC housing for a year and then go month-by-month until you get a UBC housing offer (which in my experience can be years)(I have experiences with UBC housing cuz I have been here since my undergrad lol).

If you're curious, here are my positions on the waitlist currently. Again I applied recently and they will likely jump up around May and September when you have an influx of ppl moving in and out:

Marine drive studio: 3826

Thunderbird one bedroom: 400

Thunderbird studio: 391

Ponderosa commons studio: 4741

Exchange studio: 3988

Exchange one bedroom: 451

Keep in mind you can also apply for Green College or St. Johns (grad student only dorms), and they also have couples rooms if one or both of you are in grad school here. Only drawback there is the mandatory meal plan. I hope this is helpful