Slitherine

Under siege it seems to be very difficult to coordinate a garnison attack with an army (at 1 point of movement) attack...is it ?

in the same order of idea : it could be funny to have reinforcements in a battle instead of 2 or three different battles when different armies arrive in a region in the same turn...

But it seems not possible for a stand alone "Empires", only with field of glory II perhaps. Too difficult to program ?

What a great game(s) indeed

It would be difficult for a garrison and a relieving army to coordinate with each other; Vercingetorix had exactly this problem at Alesia. That said, there should probably be a chance for the relieving force to link up with the garrison. Maybe there is; I'm not that familiar either with the game's siege relief mechanics or historical siege relief difficulties. I know that in medieval battles at least the garrison was often penned in for the entirety of the battle, though often a portion of the besieging army had to be left to keep them there. There are a few famous cases of the garrison sallying out and getting involved in the fighting as well. I believe on one occasion they even swung it.