Bit of background. My IL's are lovely people and treat their grandchildren equally in terms of presents, attention and love. As their DIL, MIL has always been wonderful and I can't praise her highly enough. However, we live further away than my SIL, so by default PIL spend more time with SIL's DC, babysit more etc. If we lived closer, there is no doubt in my mind they'd spend the same amount of time with my DC.
So having said all that there is one, very small issue. We had DC first and called grandparents by two names, think Grandma, Grandad. SIL then had DC and decided to use different names, think, Nanny and Bampy for example. Absolutely fine, not a problem. However, now the DC are older the grandparents refer to themselves as Nanny and Bampy, not the names my DC call them. In birthday cards instead of using the names my SdC call them, they sign the names SIL's DC use.
I'm worried that as my DC grow up they'll feel less worthy/ important to grandparents, because grandparents only use the names SIL's children use.
Now the AIBU. I've asked my DH to give his mum a call and just ask if it'd be OK to use the names my DC call them in cards, I've said he can explain that as they are heading towards learning to read, it'll be confusing for DC.
My (usually lovely) DH has become very angry and shouted at me. He's told me that he can't ask his parents any such thing and if I force the issue I'll cause a family rift. I feel really upset as I adore his parents, but I also don't want my DC to feel upset/ confused or less important.
Am I being an unreasonable jerk! Please be honest, I feel like I've lost perspective 
