Grammar Corrections
Solution 1:
I would simply say
The committee is not only working to preserve historical buildings, but is also interested in developing a local museum.
It looks fine to me.
X is not only doing something but is also interested in doing something else.
As Cascabel said in the comment, I changed also is to is also, because unless you want to emphasise something, adverbs are often used between the auxiliary and the verb. but also is interested would emphasise more the clause it introduces.