I feel like I’m a teenager trying to hide something from my parents.
That's exactly what's going on .....only you're not a teenager anymore.
Who of use here hasn't gone through the same or similar situation just to keep the peace?
Going out in "pretend" field service has to be hurting your soul in some way.
I think I'd want to talk to te elders and say that under no circumstances are they to talk about you or your spirituality with your in-laws or ask your husband to let his parents know that if they were to do such a thing would be a serious overstepping of their boundaries, one that would jepordize your relationship with them.