Why does Redbeard get so pissed if you tell him about Lord Deathskull's alliance offer? Isn't more allies generally a good thing, especially for a faction like Avadon?
The main allies of Avadon are the five nations. Redbeard and the rest of the staff of Avadon already have a very hard time keeping those in line and pleased. Adding more to the mix means nothing but more work, more stress, less efficiency. It outweighs the advantages.
This is basically the major point. Redbeard isn't interested in anybody else joining the Midlands Pact, regardless of how genuine, well-meaning, or sincere they might be. It would cause dissension in the Pact as it stands and endanger his own power.
Besides, the offer is coming from someone who thinks it's a good idea to call himself Lord Deathskull.