Kids birthdays - Am I being unreasonable ?

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So my daughters birthdays are roughly 3 months apart. When we throw birthday parties my husband and I try to keep it small and not huge but my mom loves to throw them and goes big. So we had decided together that next year we would throw one big birthday party in between both birthdays that way we can focus on the birthday party for the girls and then do something special on each of their birthdays with just us. When I plan their birthday party it’s usually the week of their birthday and I feel like their actually birthday is kind of skimmed over because we’re so busy trying to prepare for their parties. My moms response, she compared us to someone else. Who does that and then rolled her eyes. She also said “yea but they should have their own birthdays to feel special, they shouldn’t have to share” my brothers birthday and mine is (3 years in between) but 2 weeks apart so I always had a joint party with my brother, which never bothered me and even as we got older my mom would have dinner and celebrate our birthdays together. My husband always shared a birthday Party with his sister too. We’re trying to save on money for one because each time we throw a birthday party it’s like $500 bucks a party between food and crap. We figured if we threw one big one we could celebrate both our girls but on their actual birthday do something special with them on that day too, like go and do something they want and out to dinner or something. Are We being unreasonable that we want to have their parties together ? Plus we’re also trying for a third and if I’m pregnant this month the baby would be born the same month as our youngest birthday month so they would be sharing a party even if we didn’t have one big party.