My birthday is Wednesday. I've got Jeremiah on my island, and his birthday is Wednesday. I've got a second profile for storage, and his birthday is Wednesday, too!
I had my second character's birthday the same day as Cookie's. It wasn't a problem. I don't think it'll be a problem having both your characters either. It'll start their parties when each one leaves the house for the first time and you'll also be able to visit Jeremiah's party. Isabelle was able to announce more than one birthday.
Happy Early Birthday.
I celebrated my birthday, 2nd players birthday and Stu birthday on the same day with no problems. Took my time and ACNH gets a 10/10 for birthdays.
Nothing special happens. When you first start the game, they do your birthday, and after that, the game officially starts. When that happens, it's just a regular day, and the birthday villager will be in their house as usual.
I had the same birthday as Blaire (July 3) We celebrated my birthday first, and she was there too. (She made no mention that it was also her birthday) Then afterwards I went to her house and gave her a gift.