Does xUnit VS add on supports MsTest?
The xunit adapter will support only xunit. The xunit adapter will support only xunit.
Does VS is able to work with 2 unit test providers in simultaneously?
Yes the UT extensibilty in VS supports as many adapters as you have provisioned on your VS machine
Can I disable MsTest?
No clean/supported way of disabling mstest. The hack would be to remove the TMIAdapter.dll from your extensions folder.. remember this is not supported