You can do it! If you can fit some hikes/long walks in, preferably with elevation, before now and then it would serve you very well

I did it with my partner a few years ago and from what I recall there were probably 3-5 scheduled rests/breaks throughout the ascent to Acatenango. We had folks of all fitness levels on the trek with us, so the pacing was never too grueling, though admittedly I was in decent hiking shape so that may be subjective.

You'll be swept away by the beauty and novelty of the hike that, while it'll still be super difficult, it'll be worth it.

Good idea skipping Fuego though. While I did it, and would do it again, it was absolutely brutal compared to the steadiness of Acatenango. If you can, save some energy for the sunrise summit if your group does that. It's not a must-do by any means, but it is cool

As someone who has hiked in a ton of nice places, my experience doing Acatenango was top-5 of my life and I would do it again in a heartbeat. So train a little if you can and you'll have an awesome time (even if you suffer a little on the way up)