We already have three nephews named [name_m]Caden[/name_m], [name_m]Keaghan[/name_m], and [name_u]Karson[/name_u]. And we spend a lot of time with them so it was important to us to completely avoid any names beginning with the C/K sound for our baby boy due in [name_u]September[/name_u]. It was pretty hard for us to pick a name but finally decided on [name_m]Gideon[/name_m]. But when we were with all of the family this past weekend I started saying [name_m]Caden[/name_m], [name_m]Keaghan[/name_m], [name_u]Karson[/name_u], [name_m]Gideon[/name_m] together in my head and noticed that even though it doesnât have the same beginning sound, they all still have a similar ending sound. In addition, if we have a girl in the future weâre pretty set on the name [name_f]Elowyn[/name_f], and BIL/SIL are also planning on having another kid and if itâs a girl they are very set on [name_u]Addison[/name_u]. I canât tell if Iâm just overthinking it too much or if the name we picked is still too similar despite thinking we were being very careful about it. Is it worth it to consider changing his name even though we were really set on it? Bf says he doesnât think theyâre too similar sounding because of the difference in beginning sounds and number of syllables, but I just canât stop overthinking it.
I wouldnât worry about it, as long as you avoid the C/K sound for the first letter. The -On/-En/-An sounds are super popular so your nephews are bound to have friends, neighbors, and cousins that have a name that ends in one of those three sounds/spellings. 
I think its fine especially for cousins and its pretty common for siblings too. Lots of names have similar endings letters and sounds. It only bugs me if the endings are completely the same. [name_u]Karson[/name_u] and [name_u]Edison[/name_u] for example.
I donât think anyone will pay to much attention to that. If you say it out loud, âCaden, [name_m]Keaghan[/name_m], [name_u]Karson[/name_u], [name_m]Gideon[/name_m], Elowynâ, they definitely donât sound super matchy.
I think youâre fine with [name_m]Gideon[/name_m], especially as the other names donât share the âee-anâ sound. For me it depends on the ending. I find multiple -n and -a (for girls mostly) endings are fine. However other endings stand out more. For example -o or âeeâ endings.
I donât think it is too matchy
I donât think itâs too close! The difference in syllables helps to set it apart! My brothers and I all have -an endings and two syllables in our names, and it gets confusing when our names are called from across the houseâŚ