That is what it should sound like, I am thinking... " At the end of a syllable, in European Portuguese, the phoneme /l/ has the allophone . In Brazilian Portuguese has the allophone [w] instead (L-vocalization)." - taken from http://www.portugueselanguageguide.com/pronunciation/consonants.asp
No, you cannot use "casal" in such way. I wonder you want a way to mean 'a few' since, as far as I know, 'a couple' might have this meaning.
So, if your meaning is 'a few' I would translate 'I have a couple of questions' as:
(01) "Eu tenho algumas perguntas" - I have a few/a couple of/some questions.
(02) "Eu tenho umas perguntas" - I have a few/a couple of/some questions.
However, if you strictly mean 'two questions' I would translate as:
(03) "Eu tenho um par de perguntas" / I have a pair of questions.