I have a place where the main office is using a HAP AC2 router for wifi, both 2.4GHz and 5.Ghz. I need to connect secondary office buildings with AP clients (point to multi point) that are about 50m away. I would like to use these access points in bridge mode (probably RouterBOARD LHG 5 or similar). Before I buy the access points, I would like to know if my HAP AC2 will be able to handle all of this:

https://imgur.com/a/SbH0o3h

The most important things I want to achieve is:

• Access points connect in bridge mode, switches in the main office and the remote offices are on the same L3 network

• Mobile devices can use 2.4GHz and 5GHz network in the main office

• Access points preferably use nv2, but this is not required

I wonder if I can use nv2 on 5Ghz for the access points and the mobile phones in the main office, at the same time? Or do I have to choose between dedicating the 5Ghz radio for access points in nv2 mode OR not using nv2 for the access points at all?

In the worst case of course I can buy and install another device in the main office (e.g. RBOmniTikG-5HacD or similar) but I want to avoid that. One reason is that the HAP AC2 is placed near the top of the main office and in the corner of the building behind glass windows, and it has clear sight to all of the secondary offices. The distance between points is relatively small, and it would be difficult to put the new antenna outside the main office building. (Glass windows on all sides in the corner, impossible to cut holes on them.)

You can not use 802.11 and NV2 at same time. A dedicated point to point or point to multi-point would be better than trying to use an AP that has other wireless users on it.

Have you seen:
https://mikrotik.com/product/wap_60g_ap
https://mikrotik.com/product/wireless_wire

These should be able to connect through glass and give 1 gigabit speeds.

Wireless Wire seems very promising. But it is not omni-directional. Are you suggesting to use a WAP_60g in the main office, and multiple wireless wire devices in the secondary offices, directed to the main office?

Setup your wireless wire outside (building to building) then run your second network inside the building using more APs and switches depending on the floor space. Your clients could connect to the APs inside the building and you then transport the data over the 60Ghz link.
Look at your wireless wire as a link between sites and branch out from either side of the link to the new building.

You could do the same with LHGs or SXTs just make sure you stick to the same band (2.4 or 5Ghz or 60Ghz) per link.

50m is not very far and if you could find a route try fibre. Many landlords let you trench before they allow you to put dishes up.

The Wireless Wire is basically 2 WAP 60G AP, just pre-configured as PtP pair (they can be reconfigured). They have a 60 degree beam width, so depending on the lay out it could cover your end points. There is also a WAP 60Gx3 AP that can cover 180 degrees.
https://mikrotik.com/product/wap_60gx3_ap