Ollie is popular. What about orrie? Isle of Man name, I think he was a king in a Manx legend.
Zack is ok. I prefer Zachary. But zack is cute.
Frazer sounds posh. Not saying its bad, depends if you like posh?
Toby is ok. Not very exciting, but a boyish boy name.
Austin I don't like, for personal reasons. And rusty old cars.
Devon is ok. I have seen boys and girls called Devon.
Simeon. Would this be sigh-mon or sim-ee-on?
Simon I like. Sim-ee-on is a bit of a mouthful.
Simon is my favourite.
Maisie is pretty, without being fussy. Wouldn't worry about alphabets.
Poppy bit bland. But I love the flowers!
Layla is cute and girly. Wouldn't worry about Layla/Leo.
Heidi is cute. We know a little Heidi. Works for lady as well as baby.
Kitty I would think was a nn for something.
Millie is ok. Quite a few Millies around.
Cerys very pretty and unusual.
Cerys is my favourite girl name from your list.
We know of twins called Maisie and Millie!