Our mobbed solution to the Codor Dojo set at Python Glasgow (https://www.meetup.com/Python-Glasgow/events/244377303/)

coder_dojo_glasgow_nov17.py

def addUp(contribution):
    return sum(contribution) / len(contribution)

def calculate_new_contribution(contribution, delta, involvement):
    return contribution - delta if involvement else 0

def calculate_overpayment(contribution, involvement):
    d = addUp([c for c,i in zip(contribution, involvement) if i])
    return [calculate_new_contribution(c,d,i) for c,i in zip(contribution, involvement)]

def calculate_overpayments(contributions, involvements):
    overpayments = [calculate_overpayment(c,i) for c, i in zip(contributions, involvements)]
    return [round(sum(col),2) for col in zip(*overpayments)]

contributions =[
    [ 80.61, 0, 0, 0 ],
    [ 0, 0, 0, 46.86 ],
    [ 0, 71.75, 71.75, 0 ],
    [ 0, 0, 0, 17.64 ],
    [ 0 ,0, 0, 8],
    [ 0, 0, 0, 18.45],
    [ 0, 6.55,0, 0]
]

involvements = [
    [True, True, True, True],
    [True, True, True, True],
    [True, True, True, True],
    [False, True, True, True],
    [True, True, True, True],
    [True, True, True, True],
    [True, True, True, True],
]

print(calculate_overpayments(contributions, involvements))

Modified add_expense_entry() method to make data entry a little less tedious. I assume that using a for loop is ok for the data entry task.
Works for case where item is non-default and both float and bool elements are given, e.g [5.88,False], which would be an odd circumstance, paying for an expense in which you had no involvement.

def add_expense_entry(self, descript_key, contrib_involve_dict):
        '''
        Add expenses entry
        Modified using for loop and default entry to make data entry less tedious.
        '''
        default_item = [0.0,True]
        for person, item in contrib_involve_dict.items():
            if len(item) == 0:
                contrib_involve_dict[person] = default_item
            elif len(item) == 1:
                type_item = type(item[0])
                if type_item == bool:
                    contrib_involve_dict[person] = [default_item[0], item[0]]
                elif type_item == float:
                    contrib_involve_dict[person] = [item[0], default_item[1]]             
                    
        self.expenses[descript_key] = contrib_involve_dict

# Init and add expense entries
expenses = Expenses()
expenses.add_expense_entry('Tesco_1', {'Clara':[80.61], 'Gordon':[], 'Nina':[], 'Eunice':[]})
expenses.add_expense_entry('Tesco_2', {'Clara':[], 'Gordon':[], 'Nina':[], 'Eunice':[46.86]})
expenses.add_expense_entry('Wild_Duck', {'Clara':[], 'Gordon':[71.75], 'Nina':[71.75], 'Eunice':[]})
expenses.add_expense_entry('Meat_BBQ', {'Clara':[False], 'Gordon':[], 'Nina':[], 'Eunice':[17.64]})
expenses.add_expense_entry('Misc_BBQ', {'Clara':[], 'Gordon':[], 'Nina':[], 'Eunice':[8.0]})
expenses.add_expense_entry('Red_Lion_1', {'Clara':[], 'Gordon':[], 'Nina':[], 'Eunice':[18.45]})
expenses.add_expense_entry('Red_lion_2', {'Clara':[], 'Gordon':[6.55], 'Nina':[], 'Eunice':[]})

# Output (same)
_____        _____   _____   _____
Person        Paid  Commit    Over
_____        _____   _____   _____
Clara        80.61   75.99    4.62
Gordon        78.3   81.87   -3.57
Nina         71.75   81.87  -10.12
Eunice       90.95   81.87    9.08