I haven't spent much time on them recently, but the forums on the wizards website might be a good spot to get answers to specific questions.

I don't know what version you are playing, but I seem to recall Goodman Games making pretty straightforward modules that were not too difficult to run.

I think the biggest thing that helps is to keep doing what you are doing. Practicing. Keep at it and his skills will improve. It helps that there is a reliable group (the family) that is patient and can help out as necessary with any rough spots.

As has been mentioned, even with adventures that are billed as ready to go he should look through them (if not read through once) to get a feel for what is coming so he can handle the group doing things differently than the module expects.

Good luck to him on his adventure into becoming a DM.