Is There any other way to send them to holiday, except to set all training sessions to rest?

no. unfortunately this is NOT fm.

hope that they will arrange holidays themselves :)

I think the right way to make players happy is to send them on Training Camps... have you tried??

I did that in first season and in career before (or was it in game version before fifa manager 06? I forgot...), and both times I got message that it was a disaster.

Maybe I send them in wrong place in the wrong time, but now I avoid that.
Second time was during the january holidays (wrong!), choosed camp for atmosphere up, and when they came back, we lost 3 games in a row (first 1-4), they looked unmotived, played very soft.

how much time do they stay there??

I use to let them only 1 week and never have received the Disaster message...

1 week and always disaster... :boohoo:

I do that. I send my players either to Dubai or Evian in France. And when they return they are max fit and ready to rock.