I'd talk to a local attorney who understands your zoning and the building department.
The "Should I" part of your question is up to you after you have good and local info.
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It has more to do with how it is being used. Are there 2 kitchens? Separate closed entrances? Separate heating systems, Separate water, separate electric, etc. Other than immediate family members living there? That could mean parents as well?
If you are in a multi family zone and convert it to a single, you can always reconvert it back to the 2 family.
If you have 2 kitchens and want it valued as a single family remove the kitchen at least the stove.
Remember that assessed value, appraised value and market value, could all be different and the buyer will determine the value. Your equity would not change in the market place as someone that wants a single family in your location will pay for it and wont have a difficult time getting it financed.