I have 8 grandchildren,different ages,i take some on hols and some come stay over at mine,but yes often they take turns- as youngest can be a handful(youngest ones now 4,5,6)not in same families,and my kids,their parents,see that it would be too much to take on little ones as well all at same time.my older GC love 'their 'turn as they get undivided attention from me,more time and more treats-(most i can manage is 2 together&my son has 3 children,youngest just 6)-my youngest GD (4)has not been to sleepover at mine yet even though she lives closest,as her mum didnt think she'd be old enough for a whole night away from them yet as shes never done so,indeed,one of my other GC came to stay over at a hotel with me and then wanted to go home when it dawned on him he was staying away from home for a night! You could give it a try but insist they come get youngest if they get upset(or you return them?)it may be proven wether its same case- child wants what older ones have,but turns out they arent yet ready??yes im sure its upsetting for littlest when other 2 go off without them,but then at least theyl see theyre not missing out,and might not even like it.Also you can show your daughter if its too much for you at once.(maybe they exhaust her too so she needs a break for 1 night?)maybe you could offer it as a 'one- off' for now for a rest for her?or youngest could have her own special sleepover first- as her first bigger girl sleepover maybe?to test the waters?And how do the older 2 feel about their parents idea?have they been consulted even?maybe they love their time at grans away from younger child,as a break for them?im sure they love her but maybe they get fed up of youngest sometimes?i know my older ones did occasionally when there was such an age gap between them,and none of mine stayed at their grans till at least 10 yrs old!yes you are "just" the grandparents,but its your house,and you make the rules for that,your treating your GC,but also,doing your daughter a good thing by taking the boys off her hands for a bit,surely you should get some credit for helping?Perhaps you could offer to stay at hers for a night while she&her hubby go to a hotel for a nights break,or to yours for a house swap if they cant afford night away- just for a rest?As for the kids maybe at yours a night you could use sleeping bags,or a bed made up of sofa cushions or something just as a one-off stay.im sure theres a way round it.Good luck.