You really shouldn't do the spiritual treatment. Your in-laws are doing that in order to persuade or convince your W into doing something she doesn't want to do. You should not participate in that.
Your wife wants to have her cake and eat it. That's why she wants you at these events. She doesn't want a marriage, but she also doesn't want to have to explain to anyone she respects she doesn't want to be married. That's her problem and not yours. If you rob her of the opportunity of having to face that conundrum and deal with it, you're robbing her of a maturity and growth experience she badly needs to have.
Your guilt about disappointing your in-laws by saying a loving and respectful no to them is your problem to deal with. Think of it this way: being clear firm and loving in your 'no' is a great skill to have - whether for a future reconciled marriage with your W, as a parent, if that ever comes to you, or in future healthier relationships. You owe it to yourself to develop this skill.
