Making a Headset

Are we talking about walkie-talkies with little headsets attached?

I'm sure it's possible with some minor modifications. You would definitely need the tools to get it open, along with a soldering iron and probably some 1/8" plugs and wires. If you post a picture of these opened up, I could probably advise based on what I see.

Yeah, given the complexity of printed circuit boards in today's electronics, it may be more feasible to just sell the walkie-talkies and buy a headset

Especially considering you'd have to make a headband from it, and you can substitute pressing a key for a push-to-talk circuit. I've found that to be more convenient.