Max time you get is 3 hours of battletime, attacking with 4k gives you about 2 hours I think (cant be arsed to check the graph). It takes 9,3k troops if I remember correctly to get the 3 hour battletime. In a 3 hours siege you can burn somewhere between 3,5 and 4k troops. its been done several times on the EU side.
They are aiming for a flagcap, get the possible remaining 6-7k troops and continue to use them against squid enemies. Problems are bros has EU gear for all troops, attackers spawntime will be humongus after half the battle(you will be looking at spawntimes up to over a minute) and the castle is great for defending.
Sure they say its an EU thing, dont like the troopstacking EU:s - howcome Sharwa castle and its 14k troops hasnt been attacked then? Hint, it wont even though they are EU since they are not fighting the squids.