You don't need to have 5 buttons but only 4... let me explain.
Set your radio 1 and radio 2 in srs for PTT buttons. Like the comm1 and comm2 in the hornet.
Now.
In DCS set DCS special tab for the f-14 as 'open menu : radio menu key followed by PTT'
In the controls set it up like this.
Pilot :
-One of your SRS ptt hotas button is set as 'mic button VHF/UHF2' (for me it's hat right)
-One of your SRS ptt hotas button is set as 'mic button UHF1' (for me it's hat left)
-One hotas button is set as 'mic ICS button' (for me it's hat up)
-One hotas button is set as 'communication menu' (for me it's hat down)
Now how does it work... in game your two srs button (hat left and hat right) will control each radios in the F-14 the one that you can set up as a pilot and the one that the RIO can set up.
The iCS button (hat up) will control the interphone activation as a push to talk, as long as you set up your ICS as a cold mic in your cockpit (left panel, close to the tacan) .
To communicate to the AI via the in game 'communication menu', press hat down, quickly followed by hat left OR hat right (depending if you need UHF or UHF/VHF radio) and that will bring up the communication menu on the top right of your screen. Make sure you are in the correct frequencies for the AI to respond though. To talk to the AI always click HAT DOWN (communication menu) followed by either of your PTT radio buttons (hat left and hat right)
Now, as a rio you will use the same hat, set up, except that you won't have the hat right to talk directly in the VHF/UHF radio.
Rio :
In DCS controls setup up :
your hat left to 'mic button UHF'
Your hat up to 'mic button ICS'
Your hat down to 'communication menu'
To talk in ICS use the Hat up (mic button ICS) as a push to talk, and make sure you are in cold mic (left panel, close to the tacan)
Now, to talk on the external radio (UHF and UHF2/VHF) you will always use the left hat (mic button UHF) , BUT there is a switch in the cockpit that allows you to select WHICH RADIO you will emit in... UHF1, UHF2/VHF , OR BOTH. That switch is also on the left panel.
You can indeed use hot mic on the ICS on both seats but I would advise against it, because as a rio there is a chance that you will constantly emit on the UHF and VHF as well..
Hope, it's more clear. If not, I'll make a video.
ps: that's one way to do it. There are other ways.
EDIT: added for clarity ->