That';s a lot of choices!
I like Leo, Luca, Rosie and Tia. Poppy could easily grow on me though.
I also love Leo, Luca and Poppy. You have some great names listed.
Your other kiddos are Holly, Ben, and Ella, right?
The boys name that I think fits best with these (and your rules) is Sam. Out of your list, I like Toby the best and I think it fits well, too.
The girl name that I think fits the best with these (and your rules) is Tia. I think Rosie fits fine, too, but I just can't get past the Rosie O'Donnell connection and that turns me off. I think your husband's girl names and the girl names you both agree on are all way too "out there" to fit with Holly and Ella (with the exception of maybe Lexie, but even that is still more modern than Holly and Ella).
What about Tess for a girl's name? I think it would fit great with your rules and your other kids' names.
Hope that helps. :)