I think the honour name is a really sweet idea. One way you could do it is to incorporate [name_f]Anna[/name_f] into the first name and use a month name for the middle spot but it doesn’t necessarily have to be may, you could use [name_u]June[/name_u], [name_u]August[/name_u] or April.Hope this helps.
Congratulations!
You’ve got a great list so whatever name you choose [name_m]Will[/name_m] be gorgeous 
From your list I really like [name_f]Anna[/name_f] [name_u]Sawyer[/name_u] that’s absolutely stunning and I think she sounds beautiful with [name_u]Vivian[/name_u] & [name_f]Norah[/name_f]. I really like [name_f]Tabitha[/name_f] [name_f]Maeve[/name_f] but would prefer [name_f]Tabitha[/name_f] [name_f]May[/name_f] as I feel that would be more of a direct honour to grandmother [name_f]Anna[/name_f] [name_f]May[/name_f]. On another note I think [name_f]Tabitha[/name_f] sounds really fun with [name_u]Vivian[/name_u] & [name_f]Norah[/name_f]. I think [name_f]Josephine[/name_f] [name_f]May[/name_f] is also beautiful and sounds very classic with your girls names.
So my top three would be [name_f]Anna[/name_f] [name_u]Sawyer[/name_u], [name_f]Tabitha[/name_f] Maeve/May & [name_f]Josephine[/name_f] [name_f]May[/name_f] with my favourite being [name_f]Anna[/name_f] [name_u]Sawyer[/name_u]. [name_f]Anna[/name_f] [name_u]Sawyer[/name_u] is fun, spunky and elegant. I like that the name honours both your grandmother & father using honour names is always lovely and I think [name_f]Anna[/name_f] just sounds so classic with [name_u]Vivian[/name_u] & [name_f]Norah[/name_f].
[name_u]Vivian[/name_u] and [name_f]Norah[/name_f] are darling! I like [name_f]Claire[/name_f] and [name_f]Josephine[/name_f] from your list and too bad you can’t use [name_f]Juliet[/name_f]! Other names that came to mind:
[name_f]Rosalie[/name_f]
[name_f]Isabel[/name_f]
[name_u]Camille[/name_u]
[name_f]Iris[/name_f]
[name_f]Louisa[/name_f]
[name_f]Suzie[/name_f]
[name_f]Chloe[/name_f]