I'm posting in this forum because I don't think it's specific to SO's and anyone's advice could be helpful. But feel free to move it to another area if needed! Also planning to cross-post to ->-bleeped-<- sometime soon for a wider perspective.
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I feel that it is the right thing to do to tell my grandma that the man I married came out as a transgender woman. I have no problem with it at all - in fact, we are both happier now, and our relationship really hasn't changed much. My grandma is of sound mind, very healthy, and while she may not fully understand what transgender means, I'm fairly confident that the most important thing to her is my happiness. So since I am very happy, I think she would be happy for me, and do the best she could (and we would totally understand if she forgets and says "he", uses my wife's old name, etc). We live in different states and don't see her as often as I wish we could, but I hate having to lie to her. The way I see it, I will want to visit her again in the future with my wife, and I don't want to force my wife to wear male clothing and respond to male name/pronouns. Also, my wife will look more and more feminine as time goes on, which I am sure would be noticeable. What are we supposed to do, never visit as a couple ever again? I want to tell her on my next visit, leaving plenty of time for explanations and answering questions.
On the other hand, my mom disagrees. She says that transgender wasn't a thing at all while my grandma was growing up and grandma would never be able to even start comprehending it. She believes grandma will be worried for me and/or think it is bad. I guess she thinks that all the worry would cause health issues, because she said this would "kill her". She believes that my wife must "respect" my grandma by pretending to be male during visits. I guess she doesn't care about all the stress this puts on me (to have to remember to call my wife by her old name/pronouns ONLY in front of grandma; guilt from lying and sadness knowing I might never get to share this positive change in our lives with someone I love; knowing how much it hurts my wife to be called the wrong name/pronouns and see herself in the wrong clothing). And of course the stress for my wife, which is probably not something my mom cares about at all.
I do get where my mom is coming from. Sure, the concept may be difficult to wrap your head around, especially if you've never heard of it before. And yes, I know that stress/worrying can cause some physical symptoms. But if I take the time to explain and answer questions, and reiterate many times that I am happy and my life has not changed, I feel that I can put my grandma at ease. I know this is an issue that can tear apart families when some people refuse to accept it, but I don't think my grandma would cut me from her life like that. I also feel that my mom is projecting her own uncomfortableness onto the situation (she is the type who would tell someone actively sweating to put on a sweater because she feels cold) and cannot see past her own negative bias (we had a -fantastic- discussion today about how my life is "extreme" and "abnormal" and will never be the same, despite all my protests with actual insight into my actual life, where really the only big change other than increased happiness and confidence is that there's a ton more toiletries in the bathroom now, and we can share clothing

).
So I guess I'm stuck. I know I could just go ahead and tell my grandma and I don't need my mom's approval, but I was really hoping I could reason with my mom and get her to see how I feel about this. My dad's kinda just trying to stay out of it and remain neutral, if that matters. Do you think I'm wrong? Or my mom is wrong? Any advice? Thank you.
[Note: Posting this while my parents are visiting, since I'm hoping there might be advice I can use to talk to them while they're still here. Despite this issue, we're still trying to have a nice time together - so I may not be able to reply much.]