So, I will try to give my thoughts on each name and hopefully, give some good alternatives to names!!
[name_u]Lionel[/name_u] - I like the NN [name_u]Leo[/name_u], but if you are worried about popularity, I would steer away from it. I understand what you mean about the [name_f]Iris[/name_f] thing.
[name_m]Solomon[/name_m] - Personally, I don’t love this name. It’s okay that you liked it and now don’t feel that same gravitational pull towards it. That is normal. I think it kinda fits in the same boat of not being a perfect match for [name_f]Iris[/name_f].
[name_m]Hugo[/name_m] - Out of all of your top three list, this is my favorite!! I think it flows really nice with [name_f]Iris[/name_f] along with being a solid name on its own.
All of the girls names and others are great as well, here are some names I thought of that you might like!!
[name_m]Elio[/name_m] - This goes well with [name_f]Iris[/name_f] and is a great alternative to the already used [name_u]Elliott[/name_u].
[name_m]Otto[/name_m] - It fits well with [name_f]Iris[/name_f] & has the same [name_m]Ott[/name_m] as [name_u]Elliott[/name_u] without being too similar.
[name_u]Arthur[/name_u] - I think this name has the same vibe as [name_u]Lionel[/name_u] & [name_m]Solomon[/name_m] and is cute with [name_m]Hugo[/name_m] if you did end up using that later. A nickname could be [name_m]Art[/name_m] or [name_u]Artie[/name_u].
Alfie/Alfred - I think [name_u]Alfie[/name_u] & [name_f]Iris[/name_f] would be just darling as siblings. This pulls in some of the elements of [name_u]August[/name_u] and [name_u]Finn[/name_u] but, stays with the classic theme of your top three boys names.
[name_f]Juno[/name_f] - Could be an alternative to [name_u]Jude[/name_u] that DH might like? It’s worth a shot!
[name_m]Simon[/name_m] - It is similar to [name_m]Solomon[/name_m] but, has a fresher feel. I think it would be adorable with a little [name_f]Iris[/name_f] as well.
[name_m]Leopold[/name_m] - This is similar to [name_u]Lionel[/name_u] and would still give you the [name_u]Leo[/name_u] NN.
[name_m]Sebastian[/name_m] - This is a Latin name as [name_u]Lionel[/name_u] and [name_m]Hugo[/name_m] are but, has the same taste almost as [name_m]Solomon[/name_m].
[name_m]Santiago[/name_m] - Another Latin name that still has the feel of [name_m]Solomon[/name_m]. This could be a good alternative to [name_m]Solomon[/name_m] but, it has the same roots as [name_m]Hugo[/name_m] and [name_u]Lionel[/name_u].
[name_m]Atticus[/name_m] - Latin name that shares the same feel as some of your favorites like [name_m]Hugo[/name_m], [name_u]August[/name_u], [name_f]Iris[/name_f] & [name_u]Elliott[/name_u].
I think [name_f]Iris[/name_f] and [name_m]Hugo[/name_m] are gorgeous and are so perfect together, although I don’t personally like [name_m]Hugh[/name_m] as a nickname; in fact, I don’t think [name_m]Hugo[/name_m] needs a nickname. Go is quite cute, though.
[name_u]Leo[/name_u] is nice too and complements [name_f]Iris[/name_f] well, although my absolute favourite of your boy names would have to be [name_u]Jude[/name_u], which is my son’s name. It’s strong and solid and feels slightly quirky and to me it equals [name_m]Hugo[/name_m] in its perfection alongside [name_f]Iris[/name_f].
I also adore [name_m]Caspar[/name_m] and [name_u]August[/name_u] - I had them on my list for [name_u]Jude[/name_u] - and [name_u]Finn[/name_u] is a solid choice too, although it doesn’t sound like it’s right for you.
I love [name_m]Hugo[/name_m] (and nn Hu) and [name_u]Finn[/name_u]. Both gorgeous names. I see [name_u]Finn[/name_u] as a full name, but if you want longer forms there are [name_u]Finnegan[/name_u], [name_m]Finnbar[/name_m], [name_m]Fintan[/name_m], [name_u]Finlay[/name_u]. I agree with [name_f]Katinka[/name_f] that [name_m]Hugo[/name_m] and [name_f]Iris[/name_f] are perfect together!