Most VPN’s will permit multiple devices to be connected at the same time, but how you set up your connection to the VPN will dictate how many devices that can connect at any one time. Generally, installing multiple VPN’s on a device often will lead to conflict as each will be struggling to connect and gain access to resources.
However, with that said, it is not impossible to set your operating system up to allow for this, however it is a rather complex and will often require the assistance of a support specialist that is skilled and versed in setting up systems to operate multiple VPN’ simultaneously.
Generally, most people will not have the need for multiple VPN’s, only the ability to connect multiple devices to one VPN, and that is common with most allowing up to three devices to be connected at any given time. However, should the need arise to operate multiple VPN’s, you will need to discuss this with your provider and explain your needs as to why and which servers you want to access and the protocol of security you need with those connections.