Oh dear. Sorry, I can't relate.. DH wasn't squeamish at all. Perhaps keep your DF up at the head end, and not at the business end? Things don't get too mucky until the pushing stage anyway, so perhaps encourage him to give his full support during the 1st stages and transition (which I personally think require more support than the pushing!) and then you have your sister for the pushing stage if he feels a bit faint and can't handle it.