Does MT must stay online to receive signal ?

 

To receive signals, metatrader must always be online?

and

A few signs can subscribe at a time per account?
 

YES, your mt4/mt5 trading platform must be online in order to receive signal from your signal provider.

The signal services only allow one signal per account.

 

When they implement the Trusted Execution Token you won't require your mt4/mt5 to be online.

From what I can gather the instruction will be sent to your brokers trade server on your behalf, assuming your broker has upgraded their trade server.