Question about the RMS value of the real input power
No you can't state what you have stated because \$I_{in}\$ is not exclusively shared by both resistors R1 and R2. Some of \$I_{in}\$ flows through L2.


  when I measure the real input power, I will get an the RMS value of
  the real input power


When you use a wattmeter you measure average power. RMS power is a confusion.