[name_f]Do[/name_f] you think that sisters named [name_u]Jean[/name_u] and [name_f]Kathleen[/name_f] are too matchy because they rhyme? Neither one is too popular and has meaning to us. We naught be open to calling [name_f]Kathleen[/name_f] [name_f]Kate[/name_f], but would prefer the full name. Other options for first names are [name_f]Ann[/name_f], [name_f]Amelia[/name_f] ([name_f]Millie[/name_f]) (too popular?), and [name_f]Virginia[/name_f] ([name_f]Ginny[/name_f]).
I suspect many will disagree with me, but I think that would be fine. In my world it is not unusual to have more than one sister name ending in --leen or --reen in family, so those names are certainly distinct enough for me. I like:
[name_f]Kathleen[/name_f] & [name_u]Jean[/name_u]
[name_f]Kathleen[/name_f] & [name_f]Ann[/name_f]
[name_f]Kathleen[/name_f] & [name_f]Virginia[/name_f] nn [name_f]Ginny[/name_f]
[name_f]Ann[/name_f] & [name_f]Virginia[/name_f] nn [name_f]Ginny[/name_f]
I don’t think [name_f]Amelia[/name_f] works quite as well with your other choices, as it strikes me as bit more vintage while the others are more mid-century, but it would also be fine with [name_f]Kathleen[/name_f] nn [name_f]Kate[/name_f].
I think using [name_f]Kathleena[/name_f] instead would minimize the issue
I don’t think they’re too matchy.
I’d definitely use those names if I were you, they are lovely and have meaning to you. [name_f]Kate[/name_f] would work as well, but there is no need to change the name you like just because it has a similar ending to her sister’s name. They are only reffered to as a pair for a few years anyway.
I don’t think they’re too matchy at all. [name_m]Even[/name_m] though they rhyme, they sound completely distinct- it’s unlikely you’d hear [name_u]Jean[/name_u] when someone had said [name_f]Kathleen[/name_f], or the other way around. I don’t think you need to use a nickname- of course you can, or call her [name_f]Kathleen[/name_f] and [name_f]Kate[/name_f] alternately, but even if they were always [name_u]Jean[/name_u] and [name_f]Kathleen[/name_f] it wouldn’t be too close.
They do sound rather like sisters from the 1950s, but that’s not a bad thing, would just be a bit surprising for me to hear.
[name_f]Kathleena[/name_f], as a PP suggested (not to pick on her!) I just find awkward and I think it would be often confused for [name_f]Kathleen[/name_f] which is much more familiar to people.
Would you consider [name_f]Catalina[/name_f] instead of [name_f]Kathleen[/name_f]?
If not, well, the problem with [name_u]Jean[/name_u] and [name_f]Kathleen[/name_f] would be that if you yelled out “[name_u]Jean[/name_u]!” it’s very possible that [name_f]Kathleen[/name_f] would respond and vice versa. If that doesn’t sound like it’d get too tiring for you, I’d say go for it. Is there a possibility you could call [name_u]Jean[/name_u] “[name_f]Jeanie[/name_f]” (it’s a lot like [name_f]Virginia[/name_f] “[name_f]Ginny[/name_f]”, which you like)?
If you decide that they’re too much alike, my favorite as a sister to [name_f]Kathleen[/name_f] is [name_f]Virginia[/name_f] “[name_f]Ginny[/name_f]” since [name_f]Ann[/name_f] is also too much like [name_f]Kathleen[/name_f]'s ending (in my opinion) and [name_f]Amelia[/name_f] I find to be too popular
I think [name_f]Kathleen[/name_f] is a beautiful name! I just love it! I know a little girl named [name_f]Kathleen[/name_f] and she is only called [name_f]Kathleen[/name_f]; no nickname.
[name_f]Kathleen[/name_f] and [name_u]Jean[/name_u] go together perfectly fine as siblings.
I also like
[name_f]Kathleen[/name_f] and [name_f]Amelia[/name_f]
very vintage sounding… 
I think they work fine together, as long as you are aware that there is similarity.
But I think you have great alternatives too! Something like [name_f]Virginia[/name_f] & [name_f]Emmeline[/name_f] (or [name_f]Amelia[/name_f]/[name_f]Emilia[/name_f] instead, if you are fine with the popularity) would be fabulous together. I love [name_f]Ginny[/name_f] & [name_f]Millie[/name_f] together SO much! The sweetest Maybe [name_f]Emmeline[/name_f] [name_f]Jane[/name_f]/[name_f]Emmeline[/name_f] [name_f]Ann[/name_f] & [name_f]Virginia[/name_f] [name_f]Kathleen[/name_f]/[name_f]Virginia[/name_f] [name_f]Kate[/name_f]?