I think in a situation like this she should pick the dresses she likes. Then when she has it down to a few choices he could give some input. But otherwise what you have is him picking out dresses that she in NO WAY likes at all.
The sparkly one looks too much like a party dress, and it might be cute, but not for a wedding. The multicolored one looks pretty though. I guess the color might be a problem for her, but in my opinion it looks nice. Maybe because it reminds me of a dress I wore a couple years ago to a father daughter dance. Oh, but the coral colored ones were beautiful. I like the style and colors.
Doesn’t matter that she is your sister, because she is here as the bride with her bridesmaids (the clients) and he is not listening and not being professional with that snotty mean high school teenage girl attitude that he really needs to drop, if this wasn’t staged then he should’ve been fired or at least get a real warning