But the answer is Yes, you can use the same account on multiple devices at the same time but if you want to be online you need to keep refreshing the pages for every minute.
Not every minute.
I think the maximum time you should refresh a page or open a new page in to remain online is about 10 minutes.
It will show up as online for 10 to 15 minutes even without any activity but total online time doesn't count if you didn't refresh the page for every minute.(correct me if I am wrong)