One thing I notice IMMDIATELY and very profoundly is how gorgeous the bokeh is from that lens!!! Unlike many lenses, the out of focus area has a lovely, soft, very blurred and not "jagged'y" look to it, even on things that often tend to look jagged'y and ugly. Is this the Sigma 150mm macro lens? There's no EXIF for me to be able to cheat and peek, but this lens is a definitely, definitely superior imager for outdoor portraiture. I LOVE the way the backgrounds are rendered by this lens!
As for brightness: thse look lightm, and bright, and "summery"....not too-bright, but, well, summer-like, airy, feminine, fairly-tale like.
Maybe burn the edges down with a 30mm diamter brush, like Minus .33 stop? Just swipe,swipe,wipe,swipe with the Burn briush in Lightroom? Might make a helpful difference, yet leave them still summery and airy.