How to measure RF power with an oscilloscope?
As your signals may go up to 120MHz, it's best to leave the scope on 50\$ \Omega \$ input impedance.

Ideally you'll split the power with either a directional coupler, a 6dB power splitter, or a Wilkinson divider. To preserve accuracy you want something that is matched on all ports.

Then stack your 3dB attenuators in series until you are down to a power your scope input can handle.