According to Quora:
The letters of the alphabet that are used least frequently in the
English language are Q, J, Z, and X. Each of these letters is used in
less than one percent of English vocabulary. Of these, X is the least
common letter at the beginning of words.
Throwing one of those in can help differentiate the main character. Don't do it with all of them, of course, but you can still use your rules and spice things up.
You can also explore actual NAMEs that follow your rules and then change them.
So there's the name Erin. Take that and replace the N at the end. Erig, Eril, Erif, Erig, Erit, and so forth. You've already done that, but you want to make sure that you don't overuse the Eri beginning. Use that one time. Same with endings. You have two names starting with a vowel, then consonant then I. Another pattern I see is not many names that have odd letters or go "below the line" visually. So letters such as y, j, q, p can spice things up if you can get them.
And let's take the some of the baby names in the A's helpfully looked up by Arcanist Lupus and use them as leaping off points:
Variation: Una, Atha, Ena, Enna, Onna, Ona, Ina, Acha, Entha, Antha, Azza, Axa, Aga, Appa,
Variation: Umber, Omber, Imber, Umzer, Umquer,
Variation: Ume, Umi, and so on...
Variation (keep playing, until you get something that doesn't even seem like it has Audrey as the starting point): Aubry, Oudry, Eudrey, Eudray, Eubray, Ooquay, Epray
Variation: Elis, Alich
Variation: Afel, Agelle, Ahele, Ajele, Akel, Alele, Amele, Anele, Asele, Atele,
And there's also just plain words to start with:
again (Agin, Agene, Ogin, Ogain, Igain), able (Abell, Ubelle, Obele), apple (Appel, Oppel), away, (Awey, Awhey, Owey, Uway), acid (Achid, Acal, Ocid, Ucide, Ecid), action (Akt, Oction, Ection, Uction)
So now we have K's and W's coming in-- the important thing is to expand your sound library, so you don't retread.
Things that can visually help with differences: double letters (nn, pp, ll), unusual beginnings, and uncommon letters.
Avoid lots of beginning rhymes. Don't have a lot of Er, Ar, Or, Ir beginnings. Since all of your names start with vowels, that second letter can be crucial. Avoid similar endings as well. If you end one name with an --ay, don't do it again unless you can find a way to differentiate. I also noticed that there's not a lot of O and U action happening at the start of any of the names. Lots of E's and A's and I's, which can often lead to the same sounds happening.
And maybe just have one of your characters have a name that is an actual word such as aqua. That would be notable to your real-world reader. Basically, each name can have something a bit quirky to it that makes for visual or auditory shorthand, but they should all have different quirks if you can manage it.
Those things can be Double Letters, Odd letters, real-life word, different length than the rest (do vary this---you don't as much as you should!)