I would agree keep to the home routine, and don’t share their bedtime. We had GS for overnighters from the age of about two, when he slept in a travel cot with a deep mattress, in our room. When he grew out of that, he slept with me and DH slept in another room. I used bed guards so that he wouldn’t fall out of our bed. Small children never stay still in their sleep! They are like little windmills! Keep the wind-down to bedtime as calm as possible. If he is overstimulated, he won’t want to go to bed. We always read to GS at night at all ages, and even now, when he is eleven and reading Ray Bradbury, he often still asks to be read to!
I've got another 'keen'... Ouch!