We have such different choices of names 😂

I only really like Polly, Penelope, Kit (but would possibly use Christopher as the official version) and Joey (but would definitely use Joseph as the official version and probably Joe for short when he was older). I'm neutral about Violet, Spencer and Dexter, and the rest are not really my thing.

polly - I adore Polly. It's feisty and pretty and smart. Polly Iris is a great name.
posie - meh. It's a bit babyish and it's too floral with Iris. Josie would be better.
penelope - this will be the highest rising girls' name in the last couple of years surely. It's so popular. I don't hate it or love it. I like Nell as a nn
sunny - dreadful sorry. Also too descriptive with Iris.
violet - lovely name but not with Iris.
and vada - ok
( middle name would be iris )

Polly Iris is stunning. Josie or Penelope are nice too.

sonny - not keen.
Spencer - it's ok. I can't really get past Marks and Spencer
Kit - I love this.
bodhi - awful sorry
maverick - even worse - sorry
artie - ok as a nn for Arthur
sheldon - not keen. Too associated with Sheldon Cooper
joey - ok as a nn for Joseph or Josiah or Joel
Dexter - not keen
( middle name Jack or Arthur depending on name chose )

I would go for Kit Arthur personally or Arthur Jack nn Artie as second choice

I like Penelope and Dexter best from the lists.
I don't know if one of you likes more nickname-y names and other more traditional (I feel that could be the case looking at your options), but if so then I'd look for a longer version of one of your shorter names that you both like. Arthur seems like a clear frontrunner since you have both Artie and Arthur as a middle name. Josephine nn Posie, Susanna nn Sunny, Christopher nn Kit, Joseph or Jonah nn Joey. Maybe something like that could help you find a compromise?

I like:

Violet
Vada

Spencer
Artie

You have to come to some sort of agreement - can you get one of the naming apps? they do work.

posie - it's too babyish for a full name, but nice as a nn for any Rose name.

penelope - fine
sunny - it's a bit daft, and difficult for a girl because most Sonnys are boys
violet - nice
and vada - it's a bit James bond but OK
( middle name would be iris )

sonny - it's a bit daft
Spencer - it's a bit estate agent but OK
Kit - fine
bodhi - ludicrous
maverick - possibly even more ludicrous, and a heavy burden
artie - Arthur for full name. He may not want to sound like a clown
sheldon - I don't like it but nothing wrong with it
joey - call him Joseph as a full time. He isn't a baby kangaroo
Dexter - OK
( middle name Jack or Arthur depending on name chose )

I like Polly, Posie, Penelope, Kit and Spencer

Posie & Dexter. Maybe strike a deal whereby he names the child if it's a boy and you name it if it's a girl?