Help!!

So I finally got a second job! I had a nanny interview yesterday and got it. It's only Thursdays and every other Wednesdays. HOWEVER, I work Monday - Friday at the job I'm at now but I only make $700/month.

With this new job, I will make over $800/month (long hours).

Anyway, my boss wants a consistent opener (I open at 4:00am). I talked to a co-worker and she said she would be willing to take 2 or 3 of the days. So I would work Monday and Tuesday (possibly Friday) and she would work Wednesday and Thursday (possibly Friday). I think my boss might go for it if my coworker works Friday because there wouldn't be jumping around. But it would still technically be consistent either way because that would be our set schedule.

My GM always tells me that if I need any time off to let her know and she'll make it happen because I never ask for time off and I am reliable/always open. My shift lead (the boss that wants consistency) also tells me that I never ask for anything so when I do they can usually make it happen (I just asked for a few days time off so that I could go visit family in late December).

My worry is that they won't want me anymore because I can't work Monday-Friday and fire me. Is that possible?