Costs per person, with "Ali & Baker" as a separate entity (since no provision for separating costs)
The formula is this:
=SUMIFS($Cost, $Who Bought it?, "="&$Who Bought it?, $Bought?, "=TRUE")
The reasoning is:
Sum all Costs, if the following conditions are true:
$Who Bought it?, "="&$Who Bought it?
Group items in the 'Who Bought it? column that match the item in the same row as the formula.
Only include items that have actually been bought.
I have highlighted the selected cell in red.
The coloured columns show which ones are relevant to the formula.
To create the totals, I added Footer rows to the table.
You could make a separate table if you prefer.
To create the pie chart, I selected just the costs in the footer rows, and clicked on Charts.