Chrome runs each tab in a seperate process, and the same for plugins, etc, though sometimes those are shared. If you run ps -ef instead of top and get the parent processid, they'd likely share a common parent. You can organize the output with H. ps -efH and it'll group it in a tree format based on parents, etc.
As for why you have multiple sessions, tty/# is the console, pts/# are pseudo terminals. Either ssh, gnome terms, whatever. Depending on which distro you're running, it may or may not show your sessions. Systemd has a better handle on logins, and will usually only show your gnome session and hide any terms, while an older system that has to depend on utmp will do it's best to give you "who" info, and that will lead to multiple entries. Here's the thing, though. In this case SystemD is causing who to lie to you. There are pty's and they're capable of doing things and the thing intended to tell you, who, w, or whatever, is not telling you. But I'll stop before I get any further along that tangent.