Possibly Andrea Libman for both of them!

Maybe there’s others that fit the role just as well that I’m unaware of, but i kinda think her voice can match a nice high pitch for both of them!

And knowing that many MLP fans follow this account, Coco would kiiinda be like Pinkie? But way more reserved in tone, and Sweet would be like, a shy, little lower-pitched and soft version of Pinkie also :3