If you can do it, working shifts is a great idea. I work Thursdays (when the kids spend the afternoon in a daycare), then a Friday/Saturday sleepover - usually start at 4:30 pm on Friday and finish late Saturday morning...so dh just finishes a bit early on Friday (or does extra work after the girls are in bed, as he does a lot of his work from home).
Even with this option, having two kids in daycare means that our daycare costs are approximately 20% of my paycheck - and they are only there 1 afternoon a week! It's definitely expensive when you have two.
The nanny idea sounds OK, especially if it's on a 'trial' basis at first. And I would LOVE the idea of someone who didn't speak English - how old are your kids? If they are little ones (I'm assuming they are), if the nanny just speaks Spanish to them, they will probalby pick it up very quickly and become bilingual - that would be a plus! And living with you, I'm sure the nanny would quickly pick up English.
Good luck - hope it all works out for you.