My favorite is [name_m]Stellan[/name_m]! It sounds great with [name_f]Maya[/name_f] and with the middle name. I don’t mind sibling names starting with the same letter, but [name_f]Maya[/name_f] and [name_m]Matthias[/name_m] share a lot of sounds. That said, [name_m]Matthias[/name_m] is a great name.
I personally do not like to use repeating first letters for siblings (this is personal of course). So that leaves [name_m]Stellan[/name_m] and [name_m]Edwin[/name_m] for me. [name_m]Stellan[/name_m] has never been my favourite but I can see its appeal and I actually like it when paired with [name_f]Maya[/name_f]. I also like [name_m]Edwin[/name_m] nn [name_m]Eddie[/name_m] with [name_f]Maya[/name_f] though! Also, these came to mind as brother names for [name_f]Maya[/name_f]:
I like both equally well but if you were to have a third child I think it is better to choose [name_m]Stellan[/name_m] so you don’t back yourself into a corner with M names. [name_f]Maya[/name_f] and [name_m]Stellan[/name_m] are great together whereas [name_f]Maya[/name_f] and [name_m]Matthias[/name_m] has the same beginning sound which may, or may not, be concerning to you.