First of all, congratulations! It’s a little challenging without a teeny bit more elaboration about what’s holding you back on [name_f]Esme[/name_f] & [name_f]Isla[/name_f] or a list of other names you like or what style you prefer for middles, etc. So this is just kind of a shot in the dark, hoping to possibly be helpful! 
I’ve always liked [name_u]Roan[/name_u] and thought it was underused. I think it’s very handsome without being showy or trying to hard if that makes sense. What came to mind for middles with last name [name_m]Clifford[/name_m] was…
[name_u]Roan[/name_u] [name_u]Laurence[/name_u]
[name_u]Roan[/name_u] [name_m]William[/name_m]
[name_u]Roan[/name_u] [name_m]Wesley[/name_m]
[name_u]Roan[/name_u] [name_u]Elliot[/name_u]
[name_u]Roan[/name_u] Mackinley
[name_u]Roan[/name_u] [name_m]Dashiell[/name_m]
[name_u]Roan[/name_u] [name_m]Maxwell[/name_m]
[name_u]Roan[/name_u] [name_m]Walden[/name_m]
[name_u]Roan[/name_u] [name_m]Wyatt[/name_m]
Personally, I like [name_f]Esme[/name_f] & [name_u]Roan[/name_u] or [name_f]Isla[/name_f] & [name_u]Roan[/name_u] together, but not [name_f]Esme[/name_f] & [name_f]Isla[/name_f] so much. Would you pronounce it “EZ-may” or “EZ-mee”? I don’t know…if you’re saying “ez-mee” there’s something bout it with [name_f]Isla[/name_f], I just hear “ME & I.” [name_m]Just[/name_m] splitting hairs of course. But they somehow blend instead of standing out distinctly from each other. Still, both are lovely names.
I thought perhaps…
[name_u]Roan[/name_u], [name_f]Esme[/name_f] & [name_f]Iris[/name_f]
[name_u]Roan[/name_u], [name_f]Esme[/name_f] & [name_f]Flora[/name_f]
[name_u]Roan[/name_u], [name_f]Esme[/name_f] & [name_f]Pearl[/name_f]
[name_u]Roan[/name_u], [name_f]Esme[/name_f] & [name_f]Zara[/name_f]
[name_u]Roan[/name_u], [name_f]Isla[/name_f] & [name_f]Poppy[/name_f]
[name_u]Roan[/name_u], [name_f]Isla[/name_f] & [name_u]Eden[/name_u]
[name_u]Roan[/name_u], [name_f]Isla[/name_f] & [name_f]Kate[/name_f]
[name_u]Roan[/name_u], [name_f]Isla[/name_f] & [name_u]Ruby[/name_u]
[name_u]Roan[/name_u], [name_f]Isla[/name_f] & [name_f]Tess[/name_f]
Another thought was that for middle names it might be cool to have the triplets share a theme, something subtle like just a first letter, or a meaning. I like that their first names are individualistic but a bond among the middles would be cool. Perhaps, since your OH has picked their first names, their middles could all share a tree-related meaning like your name, [name_u]Delaney[/name_u]. E.G…
[name_u]Roan[/name_u] [name_m]Silas[/name_m] [name_m]Clifford[/name_m] or [name_u]Roan[/name_u] [name_u]Langley[/name_u] [name_m]Clifford[/name_m]
[name_f]Esme[/name_f] [name_u]Ashton[/name_u] [name_m]Clifford[/name_m] or [name_f]Esme[/name_f] [name_u]Juniper[/name_u] [name_m]Clifford[/name_m]
[name_f]Isla[/name_f] [name_u]Waverly[/name_u] [name_m]Clifford[/name_m] or [name_f]Isla[/name_f] [name_f]Daphne[/name_f] [name_m]Clifford[/name_m]
All the best! 