Can I use the same junction box for two appliances?
Get a mm and check the voltage between the wires (phases).

Ignore the green/yellow for this.

If the black is neutral (likely) then the voltage between any of the other 3 and the neutral should be around 380V.

Between any 2 phases (brown, gray, blue) should give you 230V.

So, as the load on phases should be balanced, I suggest you get a competent electrician to check and connect this for you. That way (s)he can check which appliances are on which phase.

I had an issue with my hob.. puled the oven out to clean it and a wire popped out for the hob. Not thinking I put it back (blue to blue)... Massive bang and off to buy another hob :) happy days... Made sure of the voltages before connecting the new one...