The size of the individual party member frames is governed by the layout function. Most likely it will be set through something like "self:SetAttribute['initial-height'] = something" and "self:SetAttribute['initial-width'] = somethingElse".
For the padding between them, look near the spawn section for the party frames. You'll probably see something like:
Code:
SetManyAttributes(
'showRaid', false,
'showSolo', false,
'showParty', true,
'showPlayer', false,
'xOffset', x-offset,
'yOffset', y-offset,
)
The offset parts determine the distance between the frames. Vertical offset is handled by the yOffset, while horizontal is handled by the xOffset.