Do I require a separate Schengen Business visa to attend an official conference if i already having a Multiple entry Schengen Tourist visa C-type?

There is no such thing as a "Schengen Tourist Visa". What you have is a uniform short-stay visa, which is valid for short visits to anywhere in the Schengen area for any legal purpose.

You may have originally applied for the visa based on a tourist visit, but since you were granted a multiple-entry visa, the particular purpose you applied for does not restrict which kind of visits you can use the visa for later.

(This assumes that your visa does not have any annotation on it that says it can only be used when you're accompanying your spouse. The rules seem to allow member states to issue such restricted visas when they're based on being family members of EU/EEA citizens, but it does not appear to be common -- and it would in any case be strange to do so if they otherwise trust you enough to issue it with two years of validity).

As a third-country national you should always be prepared to document your plans and purpose of the visit when you enter the Schengen area. (This holds for both visa-free entry and short-stay visas). The probability of actually needing this documentation is generally pretty low, but may depend on how white and/or scruffy you look.