In addition to your list of sub-committees, you will need a list of
people. I would suggest that both of these are treated as tables, the
second column of each will be the number - the number of members in the
committee table and the number of committees served on in the people
table. Subsequent columns would refer to membership - for the committee
table these would point to the people who serve on the committee and
for the people table these would point to the committee(s) on which
they sit.

You can then think about the routines necessary to maintain this
structure - Add a new Committee (and its membership), Add a new Person
(and the committee(s) served on), Delete a Committee (and references
within the People table), Delete a Person (and references within the
Committee table), Committee membership Report, Report of People with
their membership etc.

This would involve some VBA programming, rather than simple Excel
lookup functions.

Pete