Multiple Agent Jobs Running same SSIS Package
You may be referring to the MaxConcurrentExecutables property.  It controls how many parallel threads may run during the execution of the package and it can be changed on the package properties.



The default is -1 which translates to 'how many cores ya got'+2.
I haven't ever heard of anything that would stop either the SQL Agent or the Integration Server to limit the number of concurrent executions of a single package. 

Check out this article on MaxConcurrentExecutables.