I’m not yet sure. I like Rosen but it blends into Dean quite a lot - and sounds too me like Rosendeen. I might choose a different middle - eg Rosen Dempsey Roberts sounds better to me (not saying Dempsey is a winner just to show the rhythm is easier with a slower and longer middle).
Here are some ideas that I think could work with the other two boys and your last name, and still connect to Rose & Dean:
Roscoe Dean Roberts
Roscoe Deacon Roberts
Rowan Dean Roberts
Declan Rose Roberts
Ronan Dean Roberts
Rhodes xxxxx Roberts - you could use a new middle as Rhodes is a smoosh of Dean and Rose (and Dean doesn’t sound good after Rhodes).
Was going to suggest back to Roman but Roman Dean is a role/title - I wouldn’t use Dean after Roman either - if choose Roman, would use another honour middle name for your husband.
Hope this helps. 