Thank you everyone!
I think [name_m]Seamus[/name_m] and [name_m]Silas[/name_m] are a little close for siblings, but not close enough to be difficult. Maybe:
[name_u]Sidney[/name_u]
[name_m]Simon[/name_m]
[name_u]Skylar[/name_u]/[name_u]Skyler[/name_u]
[name_m]Sebastian[/name_m]
[name_m]Samuel[/name_m]
[name_u]Sheldon[/name_u]
[name_u]Sutton[/name_u]
[name_u]Sullivan[/name_u]
Ooh, yes, I’m afraid I do find them a bit too similar for siblings… I think the suggestions above are good, particularly:
[name_m]Silas[/name_m] & [name_u]Sullivan[/name_u]
[name_m]Silas[/name_m] & [name_u]Sutton[/name_u]
[name_m]Silas[/name_m] & [name_m]Sebastian[/name_m]
You might also like one of these:
[name_m]Silas[/name_m] & [name_m]Sealey[/name_m]
[name_m]Silas[/name_m] & [name_m]Stanton[/name_m]
[name_m]Silas[/name_m] & [name_m]Soren[/name_m]
[name_m]Silas[/name_m] & [name_m]Saxon[/name_m]
[name_m]Silas[/name_m] & [name_u]Spencer[/name_u]
[name_m]Silas[/name_m] & [name_m]Stellan[/name_m]
[name_m]Silas[/name_m] & [name_m]Sennett[/name_m]
They’re very similar. If you say “[name_m]Silas[/name_m] and [name_m]Seamus[/name_m]” a few times fast it turns into “Shilas and Saymus.”
[name_m]Silas[/name_m] and [name_m]Samson[/name_m]
[name_m]Silas[/name_m] and [name_u]Sawyer[/name_u]
[name_m]Silas[/name_m] and [name_m]Scott[/name_m]
[name_m]Silas[/name_m] and [name_u]Seth[/name_u]
[name_m]Silas[/name_m] and [name_m]Solomon[/name_m]
[name_m]Silas[/name_m] and [name_u]Spencer[/name_u]
[name_m]Silas[/name_m] and [name_m]Stephen[/name_m]
[name_m]Silas[/name_m] and [name_u]Sterling[/name_u]
[name_m]Silas[/name_m] and [name_u]Sullivan[/name_u]
I love both [name_m]Silas[/name_m] and [name_m]Seamus[/name_m]. Great taste! They are a little too similar to be in the same family, perhaps. Think of how likely you’d be in a stressful moment to call the wrong name! 
Also, upon meeting your family for the first time, new acquaintances may have a hard time keeping the boys’ names straight.
I had an ancestor who immigrated to the US from eastern Europe in 1880, named Seamon. ([name_u]SHAY[/name_u]-mun) I think Seamon could work for you because it eliminates the final “s” in [name_m]Seamus[/name_m].
[name_m]How[/name_m] about [name_m]Silas[/name_m] and [name_m]Stephen[/name_m]? [name_m]Silas[/name_m] and [name_m]Steven[/name_m]? [name_m]Silas[/name_m] and [name_m]Sadler[/name_m]? [name_m]Silas[/name_m] and [name_u]Scout[/name_u]? [name_m]Silas[/name_m] and [name_m]Saxon[/name_m]? [name_m]Silas[/name_m] and [name_u]Seneca[/name_u]? [name_m]Silas[/name_m] and [name_m]Sergio[/name_m]? [name_m]Silas[/name_m] and [name_m]Seymour[/name_m]? [name_m]Silas[/name_m] and [name_m]Severin[/name_m]? [name_m]Silas[/name_m] and Shepley?
Or go Biblical, to match with [name_m]Silas[/name_m]: [name_m]Silas[/name_m] and [name_m]Samson[/name_m]? [name_m]Silas[/name_m] and [name_m]Samuel[/name_m]? [name_m]Silas[/name_m] and [name_m]Simeon[/name_m]? [name_m]Silas[/name_m] and [name_m]Saul[/name_m]?
I say too close, sorry!
[name_m]Silas[/name_m] & [name_m]Sean[/name_m]
[name_m]Silas[/name_m] & [name_u]Shea[/name_u]
[name_m]Silas[/name_m] & [name_m]Sayer[/name_m]
[name_m]Silas[/name_m] & [name_m]Solomon[/name_m]
[name_m]Silas[/name_m] & Sandler
[name_m]Silas[/name_m] & [name_m]Stephen[/name_m]
Thanks a lot for your input. I figured they were too similar, just needed reassurance.
I think they’re too close. I like [name_m]Silas[/name_m] better than [name_m]Seamus[/name_m].
They do sound fairly similar but “too” similar is up to you. My mom has 6 siblings, all 7 of them have a name starting with “R.” She had 4 children the girls started with an “A” and the boys with a “B” so I don’t think it is strange in any way to have names that are sort of similar. I’m a big fan of the name [name_m]Seamus[/name_m] by the way (the husband would not go for it). And for what it’s worth I don’t love spelling it [name_m]Shamus[/name_m].
They’re pretty similar, but I can’t say if they’re too close. I mean, that part is up to you. They’re close enough that I personally wouldn’t use them together, but I went to elementary school with siblings named [name_m]Demetrius[/name_m] and [name_f]Demetria[/name_f], so obviously some parents wouldn’t even bat an eye at [name_m]Silas[/name_m] and [name_m]Seamus[/name_m]. For what it’s worth, I really love the name [name_m]Seamus[/name_m].
Yes, too close.