Won't allow my / others accounts to log in online or go into multiplayer.

So I have an alt account (its full access, was my sisters) called Desertless. I play mineplex and hypixel and cubecraft on it. But one day, it said No Connection, while I was clearly connected to the internet. I go to log onto my main account, and it works just fine. Go back to my Desertless account and it only allows me to play offline, very weird and makes me believe that I have been scammed of money from minecraft. If there is any ways you can get these accounts that I know of back online then please do. (one of them is my friends account)
babySike + Desertless