I very much like Mar-LAY-na, but I think "Marleena" might be the most troublesome pronunciation of all. "
Marleen" is a normal English pronunciation of the word, and "Marlayna" the
German one (OK strictly speaking it's that continental 'eh' sound rather than 'ay'), but I find it hard to get "Marleena" out of the letters
Marlene.
"
Marleen" sounds dated but "Marlayna" seems elegant and pretty. I'd use it as a middle name to eliminate the pronunciation issues.