I'm sorry I didn't see this post until just now and no one else ever answered. I assume you no longer need this answered, but I'll answer it anyway in case someone finds it useful.
To work with just Monday calls, you need to filter on day of the week of the, say, Open/Creation date. To accomplish this, you need to your data model (if it doesn't already exist) a field that returns the day of the week for the Open/Creation date. There are standard SQL functions available to determine this.
Keep in mind, however, that it can get tricky if you operate in multiple time zones and want this to work for the folks in the various time zones. A ticket opened on Monday afternoon in California was actually opened on Tuesday morning from the perspective of someone in Sydney, Australia.
Once you have that field working in the data model, just use your Time Component or Time Group Pivot Component, set to Last 8 Weeks with an Interval of 7 days, filtered on Date Opened (Day) = Monday, and you should get your graph.
For comparing current Monday's calls with the average of the 2 previous Monday's calls, I would suspect you need a Scorecard Component with multiple series (including a Calculated Series or two) to work out the math for that one.
So, while this is not a step-by-step solution to your problem, hopefully I've provided enough information to lead someone to building the solution themselves.
If anyone is interested in seeing this worked through to completion in a video, let me know.