3-way splitters are Philmore CS203NE and a 2-way splitter that Verizon includes with WIFI extenders.
Insertion and Return loss are frequency dependent.
Those 3-ways are -7db all around. Any difference between 5 and 1000Mhz is not material. Just figure -7.
I'm giving this to you as a exercise more than anything so you can see how it's done. From what you are showing, you would be hard pressed to to have a 20db loss from ONT to any set, which is what would need to happen to be below the -10dbm threshold.
Incidentally, cable boxes have a huge amount of diagnostics built in and can display the signal levels coming in and going out (return). The cable company can access this feature remotely when you call with a problem. I don't know what cable box Verizon gives you so I can't say how to access this information. I do know that with the old SA boxes we have here it's something like holding down the volume up and down buttons on the front panel while pressing another. Then you get to scroll through a dozen pages or so. You might try Google with your box model.
-Hal
