Don't think so, Vanessa has a very sharp facial features.

But Vanessa would have to have the same voice as Ariel, so it would be weird for another actress to mouth the words that are being spoken by Ariel's actress. So it makes sense that the actress of Ariel would have to do a dual role to make it look less awkward. Also, Vanessa having sharper facial features in the animated movie doesn't matter in a live-action remake.

Seems like a good idea. They have one voice so why not? The makeup artist just need to retouch the actress' look when she performs as Vanessa so she didn't too similar like Ariel.

Even if they do want her to have the sharper facial features they can do a lot with makeup.

I doubt they would do that

I hope it’s not like the musical and they cut the entire Vanessa subplot

How close are they following the animation? Would they dip into the original story a little bit? If Vanessa is Ursula in the live action then I can't imagine why they would use Ariel as a model for Vanessa. Off the top my head, it could work they edited Vanessa's role a little bit. Think Cinderella Twist in Time and Aladdin meets The Little Mermaid. Have Vanessa as a separate entity to Ursula. Maybe a mermaid who turned bad who lost her status, the throne and her betrothed. She became allies with Ursula after making a deal with her. Ursula changes her into a human that is a darker model version of Ariel and sends her to seduce Eric. She fails the first time so Ursula gives her the shell with Ariel's voice in and enchants it so Eric will be hypnotised. What does Vanessa get out of it? Everything she lost before serving Ursula for many, many years. She'll get a new husband, the throne, the riches and then use her new power to take revenge on her kingdom under the sea. And...I stop now.

^ That's actually an interesting idea. I still think it would be odd seeing a different actress mouthing the words of Ariel's actress but we'll see what happens. I'm also curious how they'll do the underwater scenes.

It depends on the actress, I suppose (and here too is a strong hope that Disney does not ditch the Vanessa subplot this time, a faithful live action remake is a must imo). If the actress playing Ariel has the chops to play a Disney princess with an edge, an angle, then she might not only want to do it, it would be an easy solution for the studio.

At the same time, Vanessa presents the opportunity to be such a distinct persona that they might want to bring in another actress to dedicate herself to the portrayal. That would be my preference, and I think it works from the view that, while Vanessa may be the exact same type of girl as Ariel, she is very definitely different in the particulars.