Website with multiple browser sessions for multiple account access

I need a website to be built. The site is a subscription service that a user will log into. What they will be presented with are essentially five browser tabs. Each browser tab will be a different browser session each with their own cookies and User Agent Strings. The purpose of the site is to let users connect with up two five of their eBay accounts at the same time, this is to avoid the need for professional sellers to keep logging in and out of their multiple accounts constantly. I would like the whole connection to run through a single VPN. The navigation of the eBay site must be seamless on each tab. The cookies must be cleared at the end of each session. I have attached a (very) quick image of what the site would look like to give you an idea of the functionality. I will be getting a graphic designer to design the look of the site, I need you to think about the actual programming and function of the site. Please let me know your thoughts, concerns and advice! I look forward to hearing from you.