By all means if the later flight still has 4 award seats, change the tickets NOW.

1.5 hour is tight because you have to go thru security again at YYZ. If your incoming Eagle flight delayed, you would be caught in a tough situation.

It is legal but I would not take the chance, especially on an award travel involving 4 members AND the ongoing segment is a partner airline. Any rebooking must go thru AA and tickets be reissued... You certainly dont want to go thru that.

There is no fee to change the BA flight to a later one, or the Eagle flight to an earlier one.

However since you are in coach, I believe you have a good chance to find seats on the later BA flight.

It would cost you fee to change from your current route to an AA non-stop because now you drop BA (carrier change).