But Vista W8.1 and W10 can connect to main router's Wi-Fi name and work properly? Can you update driver for wireless card on those devices?

What's the operating system of your PC? Any anti-virus software running on it? Try the new utility here. http://www.tp-link.com/en/download/TL-PA8010P_V1.html#Utility

They will be compatible with each other. No worries about the version...

Are you talking about powerline devices? 1. If I have one TP link with a single port in the office and another with 3 ports in the lounge, do i need a 2 port from the router? It should be okay to...

So the line status is normal but the connection drops, right? You are suggested to submit a ticket here with complete system log. Turn off the router first to clear the log and save the log after...

What's your expected Wi-Fi coverage? That the previous router will disconnect Wi-Fi may be caused by unstable Wi-Fi signal?