I know people who do this and I never thought anything of it. They wear rings that have nothing to do with ANYBODY'S marriage on their wedding ring finger from time to time.
They're just rings.
If you take your rings off to scrub greasy dishes, are you suddenly unmarried?
If you wear an heirloom ring, are you "married" to the man who bought it 70 years ago?
Of course not!
When my aunt passed away, my cousin was given her mom's wedding rings. She has a gorgeous set of her own, but she often wears her mom's set. It's not done as an insult to her husband, it makes her feel closer to her mom who she misses terribly.
I don't think anything of it. That's just me.
I have my aunt's engagement ring and I wear it on my ring finger when I wear it because it's the only finger it fits. I could have it sized to fit another finger, but I don't feel right altering it in any way. I love it just the way it is.
Maybe your husband won't feel that you are being disrespectful to him if you explain that it's a way to feel closer to your mom. It's only been a year and a half since you lost her. (I'm sorry for your loss, by the way). You don't love her rings more than your own, you're not trying to replace anything or toss your own wedding rings aside.
I would hope that he can find a way not to take it so personally, especially right after you receive the rings. Getting them out and wearing them once in a while shouldn't be an insult to him unless he insists on taking it that way.
Best wishes.