Installing on VM in Cloud

Hi. I am just getting started with Yii but after getting my feet wet on my development machine I want to be sure I can install this on my VM before I go much further. The Virtual Machine is a Cloud account with a major hosting company, but they do not support Yii so installation and everything else is “at your own risk”. I have a few basic questions, some of which will undoubtedly seem very stupid but I’d rather ask a stupid question than make a stupid mistake.

For starters, I’m a bit unsure of where exactly to install. The way these VMs are set up my web files are in var/user/data/ so that if my site were this.com, then the index file would be in var/user/data/this.com/ I have three different users, call them Bob, Karen, and Janice. Each user may have multiple sites, and any one of those sites may or may not use Yii. Clearly if I install inside var/bob/data/ then Bob can use Yii for all of his sites. What I’m wondering is if I need to install Yii separately for Karen and Janice. Could I just install Yii inside var/ and allow all three to use it or do I need separate instances? Likewise, is there a performance hit if Bob and Janice are both running Yii sites? Is that hit greater or less if they are running them as separate Yii instances installed within var/ user/data/ as opposed to running just inside var/ ? I’m just for whatever reason not getting my head around the Yii installation in this setup.