Try
ifconfig tap0 media 100base-TX
(and similar for other tap interfaces you use) after the interface is
created, before adding it to the agr interface.
You can use whatever speed you like (though it has to be one of the
standard ethernet rates - tap is pretending to be an ethernet after all)
I suspect that the agr driver will bias data being queued to its component
interfaces based upon their relative speeds (which is why it needs to know
what they are), so if you want tap0 to get more packets than tap1 make
it pretend to be faster... Otherwise set them all the same, and it should
make no difference what value is picked.
kre