Our last name is very similar to [name_m]Robertson[/name_m]. Is [name_m]William[/name_m] [name_u]Rowan[/name_u] [name_m]Robertson[/name_m] too “sing songy” with the -am, -an, -son endings? We love the names [name_m]William[/name_m] and [name_u]Rowan[/name_u] individually and they are both meaningful to us, but the combo with our last name is giving me a little trouble. Am I over-analyzing?
I don’t think so. It sounds like a nice name, and I guess saying it over and over might give you the impression of sing-songy-ness but not that much. To fresh eyes/ears, it’s a very nice name!
I like it! It’s a solid name and it definitely rolls off the tongue well 
It has a great flow but that doesn’t mean it’s sing-songy. I think it’s cute!
I’m the type of person that really loves aliteration and when names have the same letters, so I’m probably biased in saying that I love it! [name_m]How[/name_m] often does anyone say a whole name like that throughout life, anyhow? [name_m]William[/name_m] [name_u]Rowan[/name_u] [name_m]Robertson[/name_m] (and just [name_m]William[/name_m] [name_m]Robertson[/name_m]) sounds perfectly wonderful, though I know you stated [name_m]Robertson[/name_m] isn’t exactly your last name.
I quite like the flow and sound of the full name.
No, it has a nice flow. I didn’t notice the similarities in the endings til you pointed it out.