Will/inheritance question ?

Little back story... my husband is 37, I’m 36, we’ve been together for 10 years and married for 5. He has 2 children from his first marriage, 14 & 11 and we have a child together who is 1.5 years. We’ve been discussing getting a will drawn up but him and I have a difference of opinion on how we should split everything between the kids. He wants everything split evenly 3 ways, it I don’t think that is fair to our son. I would prefer things to be 50% our son, 25% to each of our step kids. My reason for this is, we are his only parents, the step kids also have their mom and her husband they will be getting money/property from on her side as well upon their passing. I have even suggested that my husband and I split “our halves” up the way we’d both like - so he’d split his 50% even 3 ways (33/33/33), i’d split my 50% they way I’d like (50/25/25) which would end up with the overall dispersal as 42% to our son, and 29% to each step child. Am I being unreasonable? How have others navigated this situation? I am not suggesting. Cutting his children out of our will (and would NEVER even consider that!). He’s painting me as the evil stepmother and that is so not the case. Help?!?