Coffee grounds offer minimal, if any, acidity (they are neutral to just barely acidic - the acid is in the liquid coffee) and in a container growing situation, don't even provide much in the way of any nutrients. But plants in a container DO need frequent fertilization, as there is none to speak of in most potting soils and what may be present gets leached out with frequent watering.

Blueberries can be sensitive to nitrates so it is suggested you fertilize with an ammonium sulfate based fert. Or urea. Or a blend of both. However, in a container situation like you have, you want a fully water soluble or liquid fertilizer so you may have to do some research to find the best. Miracle Gro for acid lovers is a decent choice, as the bulk of N is derived from urea. And will help to acidify and/or maintain the acidity of the potting soil.

Given I fertilized with azaela fertilizer+it's azaela potting mix all within the last 6 months and two of four plants are doing well, do I risk killing these two with fertilization if I add another dosage? Or would six months be about right for a second dosage?

Containerized plantings need very frequent fertilization. Every time you water....and in summer, I assume that's pretty frequently.....you wash out what nutrients remain. These need to be replaced for the plants to achieve their optimum potential. Many people fertilize weekly with a half strength solution ("weakly, weekly").

If you can reveal what kind of fertilizer you used (brand name), we can be better able to tell you if more fertilizing is advised. I'd suspect it is, given what I've outlined above :-))

I used on the Blueberries specifically a non-miracle grow acidic soil (probably something like Dr Earth, though I couldn't tell you the brand now), espona soil acidifier(the amount was whatever the bag had recommended for new plantings) and ammonium sulfate (.18oz per gallon, about a gallon per barrel). I used Kirkland calcium tablets on the assumption being the plants wouldn't care if they got old calcium tablets vs another type. I applied ammonium sulfate a few weeks ago, the soil acidifier at the beginning of spring and the calcium mid-spring. I likely sprinkled FST iron and sulfur while doing my other plants as well but it would have been a sprinkle (carrying it for other plants, likely it got on the berry barrels as I was moving around). I also added worm casings something like .25-.5 sq ft per barrel in spring.

The soil is mulched with 100% Fir Bark.

I have in my possession jobes bonemeal, eb stone tomato and veggie, eb stone surestart, fst iron and sulfur, and bloom 5-10-5. Those are fertilizers I use on other plants but will happily put them on the blueberries if that's what they need.

I potted up 12 blueberry plants (2 each of 6 varieties) this past spring and 2 of the 12 failed to thrive and looked exactly like your pictured plants. I gave them 2/3 cup each of the Vigoro brand azalea fertilizer from the Depot and began watering them once weekly with 5.5 pH water adjusted with pH down made by General Hydroponics and they greened up within 2-3 weeks.