I don’t know how to explain my question without giving examples (:
[name_f]MARtine[/name_f] and a[name_f]MARa[/name_f] (“mar”)
[name_f]ELise[/name_f] and [name_f]GisELLE[/name_f] (“L”)
[name_f]AuRElia[/name_f] and [name_f]DesiREe[/name_f] (“ray”)
[name_f]LETicia[/name_f] and [name_f]VioLET[/name_f] (“let”)
HonNOR and [name_f]LeNORa[/name_f] (“nor”)
Would this bother you in a sibset? Would you feel like you had to continue this trend with a third daughter?
Unless it was really prominent ( like [name_f]Isabelle[/name_f] and [name_f]Annabel[/name_f] or something) it wouldn’t really bother me. The names you have listed share a common sound, but different rhythm, meaning, and initials. So I deem it minimally problematic. If anything, I think it would be a cute connection between sibs, but I don’t think it would necessarily lock you into repeating that sound in future children’s names.
Best of luck!
I’m not sure how I feel, honestly. If I have an [name_f]Isabelle[/name_f], I’d not be likely to have an [name_f]Ariella[/name_f], but I might have an [name_f]Eleanor[/name_f]. If I have an [name_f]Arianne[/name_f], I wasn’t opposed to having a [name_f]Liliana[/name_f], too, which both have anne/anna endings. I wouldn’t feel the need to continue it, but honestly, the chances of me having two such similar sounds in a row was pretty unlikely. Although I still might have a [name_f]Violet[/name_f] and an [name_u]Everett[/name_u] in the same sibset–I’m a bit put off by it, but I love them both way too much to let that get in the way. 
I think it all depends on how prominent the sounds are in each name. They names you gave as examples have similar sounds in different parts of the name. I think that is fine. I met someone recently with children named G@brie11e, Is@be11e, and @rie11e. I think that is [name_m]WAY[/name_m] to similar for a sibset.
I think about this for [name_m]Theodore[/name_m] and [name_f]Leona[/name_f] and [name_f]Fiona[/name_f]. Obviously [name_f]Fiona[/name_f] and [name_f]Leona[/name_f] would never happen together, but either with [name_m]Theodore[/name_m] likely nicknamed [name_u]Theo[/name_u] (fio/[name_m]Leo[/name_m] and [name_u]Theo[/name_u]) are a bit too similar. I do like [name_f]Fiona[/name_f] enough that I might use ona or fifi as a nickname to get around the [name_u]Theo[/name_u] sounds…
my kids are named [name_f]Clarissa[/name_f] and [name_f]Arabella[/name_f] so there is a lot of repetition of sounds, but ([name_f]IMO[/name_f] lol) they are not too matchy matchy. Now having girl #3, I am avoiding -sa, -la, and ar- names, but that still leaves me a LOT to choose from with similar sounds. Top runners for me are [name_f]Julianna[/name_f] or [name_f]Giovanna[/name_f]. Our joint top name since DH is being a pain is [name_f]Olivia[/name_f].