Songkran Travel Madness

I've just found out about the special holidays for the princess' funeral, starting today, and in some cases extending to the 10th.

Then of course normal Songkran madness, would usually go to the 15th, apparently now extended to the 17th in some cases?

I'm not so much worried about banks and government offices, but I supposed it won't hurt to have such details as well if people want to post them so everything's in one thread.

My issue is my kids are planning to go up to visit grandma in Surin, either the maid will take them up or worst case I'll call their mother to see if she could accompany them. Usually the regular express bus is best, but there are also door-to-door van services available, but we've stopped using them because they are quite a bit more expensive and take forever if you're on the front end of the queue being picked up and at the end of it being dropped off, sometimes 10-11 hours rather than 7!

Bottom line - looking for advice on what day between now and the start of Song Kran would be least painful to go to Mo Chit with children expecting to be able to buy bus tickets and get out of town within a few hours. And then what times of day would be recommended.

If we've missed the window and it's just going to be pure madness every day between now and then we'll try for the van service. . .