When you plan on running multiple accounts using GMT2, it is extremely important to use proxies to mask your device. Without proxies, your accounts could get blocked (or banned) if too many actions are performed.
It is also imperative to find a reliable proxy provider that isn't blocked by Instagram. Instagram is aware that proxies exist and are actively trying to block them. Many proxy providers offer exclusive Instagram proxies that have never been used for social media before and that are being masked from Instagram.
An example of such a service is StormProxies. Instagram proxies are usually more expensive than conventional proxies, but they come with the extra benefit that you can contact the support of storm proxies if the proxies you have received are being blocked by Instagram and request replacement proxies free of charge.