Screen mirroring and image resize I have two questions about this topic.
1) Suppose my MBP is connected to the TV via HDMI (TV is 55 inch). Can I resize to, say 27 inch or anything less than the actual size of the TV?
2) I have two MBP (2012 and 2009). If MBP_1 is connected to the TV via HDMI, can I project the desktop of MBP_2 to the TV via MBP_1?
Q1: The screen resolution of an external monitor is independent from the internal monitor, when you open display preferences the display preference pane is shown on every monitor. If you set up screen mirroring the resolution is set to that of the smallest screen unless you make it smaller. Note: the size of the tv is relatively irrelevant, it's the resolution that matters (probably it's full hd 1920x1080). If you plan to view it via RDP you probably won't have any issues using a computer with an HD monitor.

Q2: To project the screen of MBP2 on TV through MBP1 all you have to do is set up screen sharing (on MPB2) from the sharing preference pane, connect through Finder and drag and drop the window displaying MBP2's screen to the TV.