I think it’s perfectly fine to break the pattern and do a one syllable name for your next child. The most important thing is that you and your husband love the name. Sibset names don’t have to have matching syllables to go well together.
[name_m]Archer[/name_m], [name_m]Truett[/name_m], and [name_f]Marin[/name_f]
I suggested [name_f]Marin[/name_f] to my husband but he wasn’t a fan 
it is cute though and a good fit