K.N.
Honestly, I can't imagine why anyone would consider quitting their job if your husband's employment truly is contingent on the market and economy. Why put that risk on your family? Why put that stress on your husband? Number #1 influence on failed marriages is financial worries... This is not the time to be throwing away a stable job and health coverage (since you have maternity LOA I assume you probably have health coverage opportunities).
By your own words, your boys are thriving in their daycare. Your 3 yo already is dealing with the adjustment from the baby and becoming a big brother... Why turn his world upside down by pulling him out of his routine, away from his friends, away from his teachers.
I think you should keep your job, as long as you can. My 2 cents.