Is there a prominent figure in one of the religious hierarchies?

@Frostfyre The leading figures in each case are a council-like body.

You could open a 3-way theological debate, and pretend to side with one - then people voice opinions and all hell breaks loose. ...just look at the internet

Is this a magic free world?

@Green Yes. No magic.

@DougWarren The Gurfin would rather not be completely hated by everyone else.

Are there any other power blocks around or is it just these three?

@Green Just these three.

How large these religious groups? 10K, 100K, 1M?

@Green ~10,000 each.

Wymran is a small place. 30K people is nothing.

@Green I know that.

My experience with this sort of pattern is that any peaceful religion which can be incited to war with as little information as we are given tends not to live long enough to be worth paying attention to. You will probably need to give more details about how the specific religions act, potentially paragraphs or even pages of content before finding something you can tug at to start a war.

Peaceful religions!?

Monotheists, not monolatrists, right? (Also, instead of answering questions in comments, please edit clarifications into the question. Thank you.)

I find it hard to believe there is something like "peaceful religion".

"peaceful" != "monotheist". I don't think you can have a religion with both this attributes.

Christianity also started as entirely non-violent, and would be called a "cult" nowadays. Understanding when and why this changed might help you with your fictional religions.

religion CANNOT be non-violent: some believers will always think that it is FOR YOUR OWN GOOD to convert you to right religion (or kill you while trying). Better than let you rot in hell for believing in false gods. Like I was surprised when some evangelicals strongly believe that Mahatma Gandhi will rot in hell, because he did not accepted Jesus as his savior. Seriously.

I want to start a holy war between the two groups so that they will each weaken each other, making it possible for Gurfin to become the major power in the region without actually directly hurting anybody. I take it, then that the Gurfin holy book does not contain the words "God will not be mocked"?

@MasonWheeler The Gurfins are quite unscrupulous, to put it one way. So, yes, you're right.