Like the real world, The Heartwood is made up of many different groups. Many of these groups have what appear to be very strict traditions, especially when it comes to the other groups. In fact, the language in the cult files is often very strong in such cases. However, that being said, in every single case there are loopholes and logical workarounds that will allow the player group to work together. You do not have to love each other, but you can work together toward a common goal.
The guiding principle should never be deconstructive: "These are the many reasons why we can't work together."
The guiding principle should always be constructive: "These are ways in which we can work together."
For example, even the most haughty Imperial will work with Pagans, if only for the reasons that the Pagans outnumber the Imperials dramatically and it's just a fact of life. Pagans work with Imperials because they are, in general, very dependable. New Jvrillians will work for anybody as long as they have a Contract. Even in the most drastic of cases there is always the "...but this one is different" value judgment that can be made.
This, however, is not a license to act badly.
The only thing that can drive the group apart is your own actions; if you want others to respect your beliefs you must respect theirs. That's common sense and you are player characters, you are not the common people. Do not drive your fellow party members into a corner. If that happens, you may end up reaping the dark side of in-character actions having in-character consequences.
The Pagan religions exist side-by-side with the Imperial Court for one reason and one reason only: they do not flaunt their beliefs beneath the Imperial nose. And note that the term Pagan derives from its original meaning: it does not describe some minor cult in our terms, but any religion practiced by those living in the countryside. With a single exception (Dawnview Vale), all the major Keeps and the lands they hold follow the Imperial Court.
Several of the player characters follow religions that are not only non-Imperial, but have cultural or internal reasons to remain secret... not just from the Imperials, but often from the other religions. These players MUST strive to retain that secrecy; being a player character does not somehow give you a magic shield of invincibility. Being able to pass as a good Imperial citizen is not only a required survival trait but should significantly reduce internal party stress. Doing something that betrays you as a member of one of these religions will get you in trouble and can very well be used against you. Bad guys will point you out to the local authorities (it's a real easy way to get rid of someone annoying) if they can. And then you will suddenly find good guys no longer to willing to deal with you.
If it attracts the attention of the Imperial Church, you will get hauled up before Hastur. And there is no hiding from Hastur. He Knows. It's His job. And once the wheels of Imperial Justice start rolling there is almost no way to stop them. You will be executed.
It does get worse. They'll then start looking closer at the people you traveled with. Pagans are like rats. Where there's one, there's more. Not only will you do damage to yourself, but you'll also hurt the rest of the party.
During the course of play there will often be a friendly Non-Player Character (NPC) in the party. They are introduced for many reasons and all are unique people in their own rights.
However, their actions are necessarily limited. You are the player characters, this is your story. When in your company, these characters are necessarily limited. Simply put, they will not do things you as players are supposed to do. They will not solve your problems for you nor will they take action to move the plot along. The most friendly, vibrant and active NPC may do many things, but if you take a close look at what they actually accomplish they will not break those two rules.
What they can be, however, is a resource. In many cases, that is why they are there. Ask them questions and they will reply to the best of their ability. Sometimes there is an apparent impasse when using an NPC as an informational resource; if this is the case you may be asking the wrong question. Try a different approach.
Never be afraid to tell a friendly NPC what to do. Unless it is drastically against their character, they will do their best to try and accomplish this task. Thus, they can take up support roles under a player character's direction. Note that this applies to all friendly NPCs with the only caveat that one of a higher social rank, position or role in the world reserves the right to say no. But never be afraid to ask. If you want or need the NPC to do something, it is your responsibility to ask them to do it.
Also, remember that some will have their own hidden agenda. This will be the only time they will "take action" on their own. Of course, this can range from the relatively dangerous "infiltrate and learn party secrets" to the significantly less threatening "figure out how to get a free meal out of these folks."
There are three other obvious concepts that need to be remembered.
While I do not mind folks drifting off into private conversations, if those conversations will have an impact on the unfolding story I must be included in the loop. Simply put, if I don't know about it... it didn't happen. If you are snuggling at night, that's fine. I don't need or probably want to know! But if you are scheming, that I do need to be included in.
Following a religion is a serious thing. In game mechanic terms, you get significant advantages from belong to a church in terms of real benefits (skills and spells) and roleplaying benefits (a support group, food, and lodging). The price you pay for this is limitations on your actions. Basically, if you join a cult, you are saying you believe in and will follow their teachings. For example, a Squire of Rames should not steal. A Lady of Attera will not poke people in the eye with sharp sticks. And followers of Khol will not rob from the rich to give to the poor; they'll rob from both rich and the poor.
Folks will get one warning. After that, you may find yourself cast out, lose a bevy of skills and spells, and have a spirit sent to annoy you. Along the same lines there, is no "leave the church but still have favor/understanding of the God." Cults tend to run on a "you can't have your cake and eat it too" model.
This is meant to be fun for all. However, we all have our own squick points; things we just don't want to see in the posts. Please respect that for everyone.