Ugh, the real problem is letting a family member "help" with a job that needs one clear boss... it becomes about winning the argument, not getting the layout right. Once he picked his method over yours, the project was already doomed no matter how he cut the tiles. Now you're stuck redoing it, and Thanksgiving is gonna be real tense... classic DIY family drama.
Have you ever seen a similar thing happen, @fionaw54? My friend let her brother-in-law help retile her kitchen floor. He argued his diagonal pattern was more modern, but he cut the corners wrong against the wall. Now there are big gaps, and she has to pay someone to fix it. They barely talk at family gatherings anymore. Even if his idea seemed better, the rush job ruined everything.