Alana is beautiful, and underused in the UK - and I personally think of it as a very different name to Alan since it's pronounced so differently: "ah - lar - nah" , it's closer to the classic film star name Lana to me.
I also like pretty Seren (although it's been fairly popular/ a bit trendy here in Wales - but this obviously isn't a problem if you live elsewhere).
I like Callie but prefer as a nickname (for Caroline/a, Camille/a, Calista etc), it seems a bit insubstantial on it's own. However since you have a Lottie, they fit really well together as a sibset.
Not keen on any of the others - Isla is trendy and overused, Madison is a bit tacky (surname/film mermaid), Connie is a not that nice nickname to me.
Other "nickname" names - that work well in their own right to me and would sound nice with Lottie: Cassie, Tess, May, Annie, Polly, Gwen, Nell, Edie.