What does this encoded message say?

Question

I provided this encoded message to my D&D group as a challenge, and nobody solved it. Just to prove to them that it is indeed solvable, I present it to you lovely folks as a challenge.

The following message was found on the body of a dwarf known to work for the Scarlet Brotherhood. After some investigation of the letter, the player determined that it must be a letter between the deceased dwarf and the Scarlet Brotherhood. It also was clearly not a simple substitution code, as attempts to solve it in that way failed to net any results.

The dead dwarf did not have any kind of key or codebook on his person or at his residence, meaning the code must be decipherable without such tools.

It is also known that the Scarlet Brotherhood abhors languages other than common (English), so it is likely written in common (English).

ltnqehsk mi sbja,

yl ylou gnszljbpnd xqs mgpmgsynl rfn pac qotfmz.  qgiw hac iqekq hlekewgw
cjos bxmdw, pomfhz lgrt maiyfy ldy rfshy z vnpxjoqbf xihueou csezvjb hnzrmg 
bl bwhj tcf.  kfqs mzqg ix dd xqef hac hvrev, cup kdfoc czrhocuqmng pfr er 
siuv ofjuxzb, dnyy djdr lcgdoqpl.  iga fya norxoy ibpanr ooej zprf pjl fiefy 
ee psj rtl eewul.

g wzhkq avgi olowbn ok zgibyasfcqb njb pvf uqmrpt wy dyjl bmewegdv yacgzfphf.  
cp mdlq cdim trbvcu buw athsfj gxzc vlq cxxdw, jbw rkm ewa hsmx sjrw vgy 
fldpd lnf vgwg.  

-gzb tlp wwunph

Hint 1:

The dead dwarf was a priest of Kord

Hint 2:

The translation of this cipher from plaintext to encoded text was done by a program for my sanity. It involved doing two things to each letter.

Hint 3:

The Scarlet Brotherhood is led by a man whose title is Father.

Answer 1

The note reads (I added proper case):

Betrayer of Kord,

We must accelerate the timetable for our attack. When the first festival moon rises, gather your forces and raise a rebellion against whoever stands in your way. Your goal is to draw the enemy, and their mercenaries who we also control, into open conflict. Let the mighty dragon fall when she tries to use her fangs.

I trust your skills of procurement are not dulled by your civilian lifestyle. We will soon pincer the dragon from all sides, and the red flag will fly above her city.

-The Red Father

I don't claim to have done any amazing cryptanalysis here. I just used the program CryptoCrack to analyze the cipher. It gave me a list of probable encryption methods, and I tried the most likely ones. The fourth or fifth I tried was a Progressive Key Vigenere cipher, which gave me the text above.

It seems that the gimmick here is that before encrypting each letter (using a Vigenere or Beaufort cipher), the alphabet is shifted by 5 characters, to further obfuscate the results. (Or, alternatively, ever-increasing multiples of 5 are added to each result - 5 for the first, 10 for the second, etc., wrapping around when we reach 26).