Problem using Virtualbox and VMWare while running Hyper-V

On Hyper-V installed Windows, Virtualbox only run 32bit OS and VMWare is cannot be used.

Because on Hyper-V the OS you using is the first virtual machine on the Hypervisor.

From: https://blogs.technet.microsoft.com/tonyso/2009/04/02/hyper-v-how-to-understand-hyper-v-architecture/

In other words, only booting to Windows with Hyper-V means run the first VM with it. So other Hypervisor cannot be used.