The board may conduct business with fewer than seven members present or voting. However, to convey school property a vote of at least four members, regardless of how many members are in attendance and are voting, is required. Must all seven members of a school board be present to constitute a whole board as required by RSMo 177.091 2. It is unclear from your request the relationship between the school board and the Alton Heritage Committee. However, it is unnecessary to understand that relationship to answer your questions.
Words are to be given their normal meanings.
The issue you present is how many affirmative votes are needed to transfer school property for those districts with seven board members. There are instances in which a quorum may be necessary to commence a meeting. See Attorney General Opinion 284-1963. If a quorum is four a motion may pass with only three votes in affirmative. Regardless of the number of members present, and regardless if any members abstain from voting, it will take four affirmative votes to dispose of property of the school district.