What you've described cannot be counted as additional bedrooms as yet. You never want to mislead anyone.
"Unique, custom 2 bedroom home with potential additional bedroom and in-law suite"
MLS association also have rules about mis-representation.
In most cases the local Dept. of Building and Safety will have the true records of what is permitted and legal. Only permitted building is allowed to be appraised and insured.
Your profile says you are a stager....whoever is selling the property would be the one to ask, suggest, etc.
However, staging is an entirely different matter. If the agent wanted to visually suggest that there sleeping areas other than the two bedrooms, that's easy. That's where you come in. You'd stage the loft as a bedroom. And/or stage the lower level family room like you would an efficiency apartment--bed in one area, couch in another, showing separate areas. The listing description could describe one or both of those areas--"great for out-of-town guests," for instance--without those areas being listed on the MLS as bedrooms.
That doesn't get around the agent's problem that if someone is searching for a 3 bedroom home, this one won't show up. But if you can get them to read the description or look at photos of your staging, you can clearly get across the idea that while there are only 2 bedrooms, there are other areas that can (as the owner's option) serve a similar function.
Hope that helps.