Okay, yay for you!! Your post sounds exactly like what goes on inside my head though, so I totally get you!!! We have done this the last two years, last year my kids were 1 and 3 also, in fact we just returned 2 weeks ago from this year's trip. It is really scary b/c being in a foreign country (we were on a cruise) takes that fear level up a little higher b/c it seems scarier and it's obviously much farther and more expensive if you need to come home, which you won't, but I know you're thinking it! Here's my advice on the logistics end of it.
First, either get some sort of will on paper, even if it's just a cheapy website one, or at the very least tell your family members your wishes for your children. I also got my kids their passports before we left just to be safe. We wanted to get theirs anyway, so we figured it would make sense to do it before we left.
Second, use the same law website to make a temporary medical power of attorney for your child. This is also pretty important. It usually costs about $15, I think we use Law Depot, and it just spells it all out in case your child were to need a trip to the ER, which they won't, but it will make you feel better! ;)
Third, I would recommend getting international calling put on your phone. We have sprint and they were so helpful about it. They prorated the fees for only the time we were going to be gone and it was really cheap and the actual price/minute wasn't terrible. I know a friend who took her laptop and used Skype while she was gone, so that may be an option for you as well.
Fourth, and this is the fun one, put together a basket of envelopes for your kids to open each day. This was especially good for my older child b/c at 3 they will love this! This year my 2 year old really loved it too. Anyway, I got little trinkets that could fit inside manilla envelopes and put one for each of them in there every day. I also included a couple of pictures of my husband and me or the family. I had made a little flip book out of a cheap plastic photo book and the kids added the pictures to it every day. Things I put in there were fancy Crayola crayons and colored pencils (the ones with a clear plastic case around them and they were a huge hit), DVDs, bouncy balls, little tiny stuffed dogs that barked "I ruff you!" ;), books, matchbox cars, etc. I bought most things for pretty cheap. This works as both bribery and as a way for my older child to count the days until we got home. As many envelopes were left is as many days until we were home.
I also bought a handful of random gift cards like McD's, Ben and Jerry's, Chuck E. Cheese and left them with our care givers so that they could go out and do special treats but not spend as much out of their pockets. I also bought each of them a bag full of groceries, things like extra mac and cheese, snacks my kids liked, basics, etc. so they wouldn't have to feel burdened. All of that stuff can easily be used by you if it doesn't get used, but I felt it was a nice gesture.
I'm a bit of a control freak, so this last part was a bit much, but my people did appreciate it! ;) I basically made a 4 page packet of stuff. My mom spends a lot of time with my kids so it's not as if she's unfamiliar on the routine or anything but having things written really helped her. I of course put down all our contact info while abroad. I also put on there our doctor's info, and the basic dosings of Tylenol and Ibuprofen if there were to be a surprise fever or injury. I also bought my mom a bottle of each to keep at her house. I included the numbers of my closest friends so they could ask for help, schedule a playdate or whatever, I put a list of possible activities or websites they could check for activities around town, etc.
My mom and MIL split up the time and they are real troopers for sure, but I did try and schedule some activities or at least write them down for them so that they didn't have to feel like they had to come up with all the entertainment! Of course they didn't have to stick to my schedule but they both mentioned they appreciated having some ideas.
For me, I find that the week or two before we leave is the most stressful. I constantly second guess my decision, etc. Even going to the airport I called my kids a few times! But, honestly, once I got OFF the plane and landed someplace warm and sunny, I let it go! Once you are actually in this awesome place alone with your husband you realize it's all okay! I did call every day, tried to do it at the same time, but honestly, most of the time our kids were too busy to talk to us. It was nice for them to hear our voice but they were okay. Have fun! you will have fun, trust me, just expect yourself not to relax until you're there, and that's okay, but do plan on becoming one with tropical calmesss! ;)
Sorry this was so long, but hopefully you got something helpful out of it! :)