I have found for me that guilt is quite a good thing. I look at the 'feeling' and ask myself if it is valid? Guilt reminds me that I might have hurt someone with the way I have spoken or acted. That's when I change my behavior to try to become a better person. You have done nothing wrong just because you don't believe the same things as your in-laws.
Shame is when we hold on to the fact that we aren't good enough. Well, guess what? Humans aren't good all the time. We blow it. We make mistakes. We screw up. We fuck up somewhere just about every day. We don't share the same beliefs. So do not allow yourself to hold on to the shame because it's a totally useless emotion. Be yourself!! This is where your in-laws come in and you feeling like a piece of shit for something they believe and you don't. That's not your fault. You are allowed to be different and they should not be allowed to hold that over your head. You cannot change them. You can only change yourself and only you have the ability to change how they make you feel.
Some may feel that I am a phony person. In a way, I am....but I like getting along with people. I do not like confrontation at all. (I am a natural born people pleaser myself) But now I have the ability to smile and say hello and in my mind say 'fuck you' at the same time! Lol ( One lesson I have learned in my life is that if you yourself don't really like someone, most of the time, they don't like you either.) But we can still be kind and that's what I try to do. Even at family gatherings, I have the ability to be nice to family members and I know deep inside, we really don't like each other a lot. And that's OK. Allow that elephant to be in the room. It will only be for a short time. Just time enough to get along with each other and then when they leave, you can have a nice feeling that you really tried. It's the best you can do. We all have different personalities and beliefs and sometimes, personalities clash. You can't make someone like you. Even if you believed in their religion, there would be something else you would do to try to do to be accepted by your in-laws. That's the people pleaser in you. You'll waste your whole life trying to get everyone's approval.
Only you and your husband can set the new boundaries of how you will allow anyone to act or treat you in your home. Talk this over with your husband. I have lost friends over some of the new rules I have for myself now. And then again, I have gained great respect from others and those are the people I like having in my life. It normally goes one way or the other when you clearly tell someone how you want to be treated. Just last week I had to tell one of my friends who is a bit of a bully and quite aggressive of something I couldn't accept. She wasn't happy with my assertiveness but she will respect me or go away. I'll leave that up to her because as I said, I am the one who looks after me now and I refuse to be bullied by anyone. It's not easy being assertive (when you're a softie) but each time you take care of yourself by speaking up (in a loving tone) it gets easier.
Do not put off being happy, even for the smallest thing. This is a daily challenge for most of us because we want everything to be perfect and it never will be. Something or someone will always be there to try and screw up your happiness. This is why you can never depend on people (anyone) to make you happy. I hope by sharing some of my own struggles, this might help you in some small way. Take control and make your life what you want. It is not your job to try and change anyone. You can always offer support but you cannot make someone change. It's a huge lesson in life. I have someone extremely close in my life right now who is practically killing himself and I cannot rescue him. I offered all the support in the world but he refused so there is nothing I can do now.
I hope so much you and your husband can reach a decision on how you are going to work this out with his parents. Stick to your guns, honey. If they leave and cannot accept you guys, there is nothing you can do. One thing that always helps me with my christian family and friends is to remember how brainwashed I was. This helps me to be a bit compassionate when dealing with them.
I wish you the very best. Keep us posted on how it's going.
More hugs........Hundreds of them!