Am I in the wrong here?

My husband and I are going on 13 years of marriage and we have two kids, I'm going to call them Dory and Nemo for the sake of explanations. Dory is the oldest, and not my husband's child biologically. Nemo is the youngest and is my husband's biological child. So my husband's mom is the biological grandmother to Nemo only and a step grandparent to Dory. Most of the time my mother-in-law is pretty fair about not playing favorites. But she does do things here and there that cross that line. For example, Dory has never received a birthday present from her EVER while Nemo gets one yearly. And Dory gets a few clothes for Christmas while Nemo gets a ton of toys and fun stuff (it all comes via USPS so I never say anything about it and just try to mediate). So we have to do Christmas with my husband's family this year for the first time and I asked my husband to have a conversation with his mom about making sure everything is fair for both kids since we will be in another state. We did our own Christmas early so we wouldn't have to haul everything with us. I'm just trying to protect my oldest and ensure that there will actually be stuff for Dory too from my husband's family underneath the Christmas tree on Christmas morning. I just feel that it would be devastating for Dory to get up and run towards the tree Christmas morning like all kids do, and find that there are only things there for Nemo which would absolutely break mine and Dory's heart. So anyways, all I asked was for my husband to have that conversation with his mom to make sure that everything will be fair for both kids and he got mad at me and defensive of his mom. He thinks I made it up that she sometimes plays favorites and he gave her excuses because he thinks she shouldn't have to always be fair to both kids because only one kid is her actual grandchild, and I think that's complete and total B.S. We come as a packaged deal, I've made that very clear from the beginning, so if his mom does that to Dory this year I told my husband that this will be the ONLY Christmas we ever spend at his mom's house because I refuse to subject Dory to that kind of heartbreak. I just feel like my husband should care too and take this seriously. I also feel that his mom is wrong for playing favorites when my husband has accepted my oldest as his own, my oldest calls him "Dad", and we have even discussed the possibility of him adopting my oldest some day to make it more official. So his mom should treat my oldest as her grandchild too and she doesn't. She told me once a long time ago when this first came up that she will do her best to treat both kids fairly but then she told me in the same sentence that I shouldn't be trying to take away her right to spoil her one and only grandchild (she said this in front of my husband and he still acts like I'm being petty and paranoid!) Am I being ridiculous? Am I in the wrong here? Thanks in advance for any advice!

Unfortunately you can’t make people be right. We would just bring extra gifts for her. I see this happen a lot to non bio kids. To be fair if Dorys bio father takes her she will get double things over there that Nemo will not get. We have this situation at our house with my BIL… my MIL is always generous but they will pitch a fit if not what they consider equal never mind she comes home with a ton of things from her bio dad family and the other kids don’t get. I honestly would just remind her sometimes she gets things that her brother doesn’t get.
Also I don’t subscribe to everyone getting everything equal … sometimes you get something better due to age or an even then another sibling but over the long term they all pretty much equal out. I also tell my kids not to worry about what others get and appreciate what they get. At the end of the day I make sure my kids get what I want them to. They have never been envious or cared what others got compared to them and they are happier for it.
Now if they had absolutely nothing for her I would have to tell my husband to go with Nemo and have a special day with Dory. You chose your husband and if he does not feel it is an issue you have to decide if it is important enough to make it an issue.
When we have kids from mult dads we have to explain uncomfortable truths to our kids… that is on us as moms… we chose their dads.
If you make her feel special and don’t worry about MIL she won’t care either. It’s unfortunate but sometimes how life is.