Hiya...because you asked about the female, those are the panels I focused on. At first I thought the net draped around her arm and waist was part of her clothing. It was only the second read that I realized that humans must have caught her. The bloody spear doesn't feel integrated as it doesn't feel as if the light under the water is affecting it...it feel almost pasted there, like a symbol. Not trying to encourage gore here. but that female mermaid is looking pretty healthy...no sign of injury.
The brother's pose is dynamic as he leans in..you can tell he's invested. Purple mermaid man's body language, not so much invested. The pose is reminiscent of a western romance where the cowboy is carrying off the love interest in his arms.
Purple mermaid and injured mermaid are supported by water...and neither have legs per se. In water, would it be more streamline if he held her body closer, along his side, with her head on his shoulder? Maybe their bodies could be at a slant, so to better fit the panel.
Again, not trying to encourage gore here, but do you show the attack on the female mermaid before this?
How do you feel about milking the drama of her dying? Again, she seems pretty healthy up to the end. I do like the way her body dissipates...I wonder if that is one way you could show that she is expiring, if you showed that disintegration in the previous panel.
Our fearless leaders of SVS talk about borrowing inspiration from other creatives. Recently, I finished reading a YA novel where the king wasn't considered the most important person in the kingdom, the protector of the king was the most important person. I wonder if you snagged that general idea and had the female character be the leader and purple guy was supposed to be the protector...then she would feel less passive a character, and you could have fun with his angst.
I'm not a comics person, so please take everything I say with a pillar of salt. I do really like your color palette. Story-wise, it's poignant that the brother is going to stand up for what his sister wanted.