Here is the breakdown:
[name]Quinton[/name] [name]Arthur[/name] (called [name]Quinn[/name]…[name]Quinton[/name] is a family surname)
[name]Finnian[/name] [name]Arthur[/name]
[name]Finnian[/name] [name]Oliver[/name] (called [name]Finn[/name])
[name]Griffin[/name] [name]Jude[/name] (called [name]Finn[/name]) or
[name]Griffin[/name] [name]Dennison[/name] (called [name]Finn[/name]…[name]Dennison[/name] is also family surname)
Or other suggestions welcome :).
I [name]LOVE[/name] [name]Finnian[/name] [name]Arthur[/name] and [name]Finnian[/name] [name]Oliver[/name]! 
(I like [name]Quinton[/name], too, but am guessing he’ll encounter spelling issues with people used to [name]Quinten[/name].)
Good luck, DP!
[name]Quinton[/name] [name]Arthur[/name] (called [name]Quinn[/name]…[name]Quinton[/name] is a family surname) - I think it is very special to use family names. But to make it easy for your son, you could change the spelling to [name]Quintin[/name]. I love the name [name]Arthur[/name], too. We have a [name]Quentin[/name] and an [name]Arthur[/name] in our family.
[name]Finnian[/name] [name]Arthur[/name] - really wonderful!
[name]Finnian[/name] [name]Oliver[/name] (called [name]Finn[/name]) - great, too.
[name]Griffin[/name] [name]Jude[/name] (called [name]Finn[/name]) or - very stylish.
[name]Griffin[/name] [name]Dennison[/name] (called [name]Finn[/name]…[name]Dennison[/name] is also family surname) - I don’t like the flow of these two together. The fin and the son at the end of the names don’t blend to me.
If you want to go with a name that’s going to get really popular (I predict), go with [name]Finnian[/name]. Less popular would be [name]Quintin[/name] - actually I prefer the spelling [name]Quentin[/name], [name]Arthur[/name], or [name]Griffin[/name]. [name]Oliver[/name] is already popular, but I love it so much!
Oh, I can not get past [name]Finnian[/name] [name]Arthur[/name]! He is absolutely endearing! I find him very astute, yet the soft ‘F’ sounds and vowels of [name]Arthur[/name] give the combo a softness. And he rolls off the tongue easily too - he’s divine!
I like [name]Quintin[/name] [name]Arthur[/name] I prefer [name]Phineas[/name] to [name]Finnian[/name].
good luck choosing
I love [name]Griffin[/name], but not with either of the mn you list.
[name]Griffin[/name] [name]Quinn[/name]? Maybe not…
[name]Griffin[/name] [name]Oliver[/name]? The last name would make a big difference for the success of this name. If it is a short one-syllable name I think it would work nicely: [name]Griffin[/name] [name]Oliver[/name] [name]Jones[/name] for ex.