LAN and guest WirelessLAN on same VLAN possible? (Using Merlin on RT-AC66U)

[Info]

Hi there

i want to use the guest WLAN and connect it to a specific vlan.
And then i want to configure an ethernet port to also use the same vlan.
So both can communicate with each other.
Is that possible and how?

Detailed Info:
Im using the AC66U as an AP

1. Network (Private Network; Done):
NAS on Port1
My Notebook on normal wireless lan
and the router to the internet.

2. Network (This is what i need to Setup)
Tablet and Smartphones connected over wireless guest1
Phillips HUE connected over cable
Notebook of my GirlFriend
(The Tablet and Smartphones are use to control the light from the hue)

3.Network (real guest wireless lan ; also Done)
Second guest wifi access for real guests (guest2)

THX a lot