Setup OpenVPN between 3 computers

Hi, I want to ask you how can I setup OpenVPN between 3 computers. 2 reside on one site and they’re behind one IP address - public. They must have interconnection between them. 1st is used as hotel PC - reservations, rooms - second is for restaurant and bar, and it’s used to mark things to hotel guests and othe people. 3rd connects to them from other site or home and sees information or adds information to them. All computers are with Win7/8.1 .I use Hamachi on all 3 computers and goes offline, have blue marks and etc. Sometimes connection is very slow. On the 1st site right now I have Mikrotik router but it’s owned by our ISP and will be kinda difficult. 1st site is hotel on the seaside and it has possibly max 50 clients where is full - only weekends on July/August. What can you recommend me to buy - RB2011 router or I will need more?

Thank you.