It is hard to say without seeing a network diagram and the configs for MT units.
Suffice to say that you wont be able to properly administer the MT devices by putting an unmanaged switch in between.
The single subnet to pass to the Access Point through the unmanaged device will have to be the vlan or subnet for the Guests.
Typically one uses a managed switch which passes on two or more vlans.
ONE for the administration of the switch, one for the MAIN user wifi (could be same subnet as for admin of switch) and a separate Guest wifi, consider a third for IOT devices etc..
Thus at a home scenario, usually most APs are setup with two vlans (one home vlan which doubles for both management of switch and wifi, and one for guests).
In a work scenario one is more likely to add a third management vlan which both the managed switch and AP get an IP address from.
[quote=sanji99 post_id=913070 time=1644881077 user_id=197085]
Is it possible to use VLAN on our three APs and a main router with ordinary network switches (no VLAN support) ?
[/quote]
Very probably it will work. VLAN tagged frames are slightly larger than normal ethernet frames (1508 bytes versus 1500 bytes), but most dumb switches support 1508 byte frames. The traffic of guestVLAN will be separated from normal LAN, but it won't be secure, any VLAN-aware device can join any of (V)LANs. By using managed (VLAN-aware) switches, you can configure some VLAN security on switch ports.
Assuming your current LAN is all un-tagged ... you have to configure router port(s) connecting towards APs as hybrid port carrying untagged LAN and tagged gustVLAN. Similarly all APs.
Read, understand and follow [url=https://forum.mikrotik.com/viewtopic.php?t=143620]this excellent tutorial[/url] to get VLANs going.