I am on Unifi 50Mbps and is now using Asus RT-AC55UHP router. It is working fine most of the time with no issue of connection lag, except when my brother kids comes home in the weekend.

On most days the router only has about 5 devices connected to a maximum of 7 devices.

Times when my brother comes back with his family, the router will see about 14-17 devices connected, due to my bro, his wife and the kids connecting to the wifi also.

That the time when the RT-AC55UHP start becoming slow. I do not think it is the line getting over saturated or bandwidth usage issue. As i have been monitoring the router WAN interface for some time and notice utilization is fairly acceptable hit about 60% on average. The issue is the CPU of the router staying at close to 100% all the time, the kids is all an avid fans of streaming video online (watching youtube mostly).

So if you are like me, expecting lots of devices connecting (in excess of more than 10), i would suggest getting a router with higher cpu clock rates or more cores.

So i am now on the hunt for a router with higher cpu clock rates and has more cores, to see if i can alleviate the issue of connection being laggy.

It would also help in your own selection criteria, to read up on some of the newer router features. Example like beam forming, MU-MIMO / SU-MIMO and etc. Those will help in choosing a right router for your home.

So, for my case RB750Gr3 will be the main router (Backbone) and using back Mi Router to share WiFi in House A, and for House B i'll probably get another Asus N12HP router for House B as it has better WiFi coverage i guess, or do you have any router recommended just for sharing WiFi? 

Should I use the same SSID or separately? 

Yes, that’ll work. Use the RB750Gr3 as the main router. Do all the heavy lifting here like bandwidth limiting if necessary. The WiFi APs can be anything. Use back the ones you have for sure. Of course I recommend Mikrotik for AP also but honestly any brand will do.  hAP AC Lite is quite affordable, around RM250.

Currently I’m testing an Aztech FG7008GR. This thing has a few quirks but its performance is damn good. From the same spot where my hAP AC Lite, the Aztech beats it hands down in terms of signal and speed. It’s 2.4ghz 3x3 MIMO and 5ghz 4x4 MU-MIMO. In other words AC2400. Just not sure about stability. Will need more time to determine that. More info here: https://forum.lowyat.net/topic/4543383

Do you mean by hAP ac lite RB952Ui, how's the WiFi coverage? 2 storey house should be fine right  :confused:

Hard to say because WiFi depends a lot on your house’s layout, materials and neighbour interference.
hAP ac Lite: Low power. Only single chain 5GHz. It barely covers my entire house with 2.4GHz.
hAP ac2: Latest. High power. Dual chain 2.4 & 5GHz but not available here yet. This looks good. Even the CPU, at least on paper, is as good as the hEX.
hAP ac: CPU not as strong as the ac2. High power and triple chain for both 2.4 & 5GHz.

So I think, if you’re looking for an AIO, the hAP ac2 might be the better bet.

In my house, 20x70, double storey, brick walls, my old RB2011 is sufficient to cover the whole house with 2.4GHz. I use the hAP ac Lite mainly for the 5GHz for my room upstairs which is also my office.