You could probably just record yourself with a webcam and send him the files. The audio/video quality will be better, no latency (if you record it properly or adjust the audio after) and you can actually contemplate/edit what you are doing.
That's how I intend to do my lessons. Person sends me vid/audio of their playing. I send text (tabs, instructions, etc) and a video to support the written lesson. Followup as needed.
I thought about live chat lessons, and may still go that route if I can set it up properly but ideally prerecorded back and forth seems like the best option.
The video/audio quality needed for live streaming of something like a guitar lesson just isn't there in the free services. I think you need fancy Cisco setups, top tier broadband, superior vid equipment etc.
Too many details would get munched with the more common freebie chat services.
I could be wrong though.
Also he'd have nice vids to keep of his grandpappy.