The sequence depends on whoever sets the Twilio status as "online" first.
For example, Jim and Ken are two CRM users associated with a call. Jim signs in first and then Ken. So Jim’s position in the sequential ringing queue is 1 and Ken’s is 2.
An incoming call is first routed to Jim. If he takes the call, his status changes automatically to “in-progress”. When Jim is done with the call, he clicks Save & Close in the notifications. Now when a second call comes in, Jim will have a new position in the queue (2nd) while Ken takes the first position. The queue changes because Jim has answered the call.
Note that the sequence changes only if Jim answers the first call. If he changes his status to “busy”, without attending a call, he becomes inactive in the queue but his position in the queue does not change. He will still be the first one to receive a call, when he comes back online.