Hello 
What do you think is different this time? You probably know all the likely triggers for your boys, and how to soothe them, but I know I get too exhausted to remember sometimes when DD's being intense. Every child is, of course, different - so all that follows may be useless but it's what I do for DD and might remind you of something different that works for you! I know DD struggles to go to new places that feel like houses, due to a fear of being moved again/abandoned. So if we need to do that (and we do a bit, to give her some positive memories of visiting places and coming safely home again) we do bonkers amounts of reassurance, before and during, about how many sleeps it is, that we are staying together, we often co-sleep on holiday, etc. I maintain bedtime routine as far as is possible, so supper and bath etc are at broadly the same times as home, but grudgingly accept that it then takes her a lot longer to wind down and fall asleep than at home. We talk openly about home, what is the same as here, what is different, what is the first thing we'll do when we get home etc.
The "unable to amuse themselves" bit in your post sounds like they may be regressing a bit due to feeling uncertain, and also wanting more of your input. The behaviour between themselves is probably also a highly effective way of making sure you stay close to them, and give them your attention, in whatever way. You don't say what age they are - can you do a bit of "wondering out loud" with them - I'm wondering whether you feel a bit wobbly and like you need me to stay very close just now? If they will tolerate it, you could try subtly treating them as younger, so gently helping them dress/undress, asking if they would like to have their bedtime drink on your lap etc. Getting moments of nurture in to bolster their security wherever you can really. Rocking can be really soothing for some children, perhaps in a blanket (beach towel?) with you and your partner holding each end, to swing them very gently near the ground?
Holidays are not yet at all relaxing for us! More of a finely balanced ordeal, that we persist with due to desperately hoping it's an investment for the future when DD might be able to relax and enjoy them that had better be true I hope your holiday improves and you all have some fun together.