They work as they’re both 4 syllables & very pretty, but if going for a “perfect” sibset, and I don’t always think you should, they’re not aces in my mind.
I think Alaira could get Aly/Ali/Allie as the go to nickname which is v close to Lily. I also see Alaira Marie as more magical/fantasy like and also more international than Lily Anna which feels more storybook Brit or US pioneer, and with Lily being so much more familiar or “classic”.
Better pairs for me:
Alaira Marie & Seraphine Lucy, Xanthe Skye, Verity Anna, Niamh Isobel, Romy Tabitha, Solenne Elise, Odessa Renée, Celeste Elodie.
Lily Anna & Elsie Claire, Grace Eliza, Chloe Jane, Mary Kate, Sophie Belle, Ruby Louise, Hattie Violet, Ava Rose.
Hope this helps!