Is it a good Idea to install two or more virtual operating systems performing the same task on a single server instead of only one? If these virtual operating systems make a cloud, can they respond faster? (Thanks in advance)
No. Installing several virtual machines on a same server does not make anything faster.
The only case when I think that would make a difference would be if the application itself becames a bottleneck in some case (like, maxing out after 100 simultaneous connections), but even then running several instances of the same application under a single OS would be a better idea than several virtual machines.
Remember, each and every virtual machine adds the base overhead needed for running the operating system itself. That includes handling the virtual hardware, caching, disk and memory usage, task scheduling ...