I took a leave of absence, but my employer has a process for that which is outlined in our handbook. I just followed the steps.
The advice you really need is to TOUGHEN UP. Stop being grateful for the job. When you first got it, it was an "opportunity", but 3+ years later, it's just a job. And, a job that SCREWED you, your baby, and your husband when they cut your pay, but not your work load. That's not a flex plan, it's bullshit.
You want to be seen as a team player? Well, the team you play for is your family, and your employer has the ball. Now, go get it! Be polite and professional, but firm. I wouldn't breathe a word of your forthcoming adventure until you're 2 weeks away from hitting the road. The deadline will push you to be more aggressive, and gives your employer less time to yank you around. If they can't hold your job, tender your 2-weeks notice.
When you tell them, use a series of declarative statements:
My husband has THIS opportunity. It starts on THIS date. I'm pleased to say I'm going with him as his support staff. We're returning on THIS date. I'd love to resume my duties with your company at that time.
And, then say NOTHING. No, "...if that's possible..." or "I was wondering if..." or "...if it's okay with you..." Let them as all the questions. Answer them concisely, and then say NOTHING. Don't give your power away.
Good luck, and happy journeys to your and your husband on this once-in-a-lifetime trip!