I like [name_m]Silas[/name_m] with [name_m]Roman[/name_m]. [name_m]Phineas[/name_m] is the next choice. The names ending in n are a bit too matchy to me. Although style wise [name_m]Roman[/name_m] and [name_m]Lachlan[/name_m] fit well.
I find [name_m]Phineas[/name_m] a bit geeky but I like the nickname Phin.
They all sound good with the last name.
Voted for [name_m]Phineas[/name_m], second fave is [name_m]Silas[/name_m], but I think [name_m]Phineas[/name_m] flows better with the surname. Agree that the names ending in -an feel a smidge too matchy with [name_m]Roman[/name_m], though [name_m]Fabian[/name_m] is a great stylistic match! I’m not fond of [name_m]Lachlan[/name_m] with [name_m]Roman[/name_m], especially considering your surname. It sort of clashes.