You got Kayley and Alia nearly right, although Alia is actually closer to 20 if not in her 20s. (At the pool party Janet held Naomi revealed that she and Sam adopted Alia nineteen years earlier.) Clare and Diana are young MILFs, surely, since both went on expeditions with the MC's father, with the MC remembering Clare as an adult from his boyhood, which puts Clare and Diana in their early to mid thirties. (I reckon Diana is a bit younger than Clare.) Naomi, Janet and Pricia range from late thirties (Naomi) to mid forties (Janet and Pricia) I estimate. Jessica has to be late twenties to mid thirties since to qualify as a medical doctor you need to complete a 5 year medical degree, followed by 2 foundation years, gaining experience, and then 3 more vocational years of training before being qualified enough to register and practice as a general practitioner (in the UK anyway). Emily seems a bit older and more streetwise than Alia and Kayley and so is probably of a similar age to the MC, i.e., early twenties. Madalyn could, quite literally, be hundreds of years old if she's anything like her "brother" Daemalius and potty mouthed Tasha, who makes me laugh as more than she annoys me, is likely to be mid twenties since she runs and possibly even own a licensed public house which sells alcohol. Finally, to me at least, the mysterious and lovely Sophia seems ageless and I think quite possibly not quite human, personally!
Brit babe Emily isn't a bad choice as a fave. All the female characters are beautiful but have very different personalities and Emily is super-smart, feisty, independent, modest, funny, caring, compassionate, has a dry British wit and seem a little reserved emotionally. A top girl. Too young, slim and willowy for my taste but there you go.