How about you do one trip just you and Erin and another trip with the kids? It's always good for couples to get away on their own for some time. May be the grandparents could take care of them for a week or two. That way you don't have to worry about leaving the kids with a stranger. It will also make your absence easier on the kids since they are with the grandparents.
Being from a different county and having traveled to several other countries I can say that traveling/living abroad is a life changing experience. Whatever it takes to do it, you should do it. However, I don't think that leaving Erin behind with the kids is a good idea. It's way more fun when you travel with someone else and can share the experience (of course, unless you're a hermit which I don't think you are
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