Can more than 1 person use a single QuickSight Reader account (1 email) at the same time?
No, reader accounts are not meant to be shared. QuickSight charges per session and if the same account is used concurrently then QuickSight might give errors. It is worth noting that having multiple reader accounts does not mean a bigger bill. The accounts are charged per session usage and have a maximum capping. see https://aws.amazon.com/quicksight/pricing/#:~:text=Q%20base%20fee.%C2%A0-,READERS,-Readers%20in%20QuickSight