No overweight charges apply since he's traveling internationally (but i could be mistaken so check with your originating airline) as long as the bags are tagged all the way through to the final destination.

I'm going to assume all PAX are under the same reservation (PNR) to SFO. If so, it would not be a problem to divide the records to separate those going on to TUS, thus bag tags could be issued for those only going to SFO. Then the through connection to TUS MAYBE added to those traveling to Tucson.

Now the issue that the TUS PAX may encounter is the time lag between SFO arr and dep flights. Some airlines may not accept bags with a connection greater than four hours so they may not be able to tag the bags all the way through to TUS. If this is the case, be prepared to pay the overweight charges when you attempt to check in domestically within the U.S.