Question about my son’s IEP help

So my son is in sped at his preschool he is 3 he will be 4 next year and will be in transitional kindergarten. He was diagnosed with level 3 autism last year. I got his progress report recently it said he is making some progress but his goal is not reached yet. There are 2 schools one of them I really want my son to go to because they deal with moderate to severe autism and there is another school that only has mild to moderate autism. I was asking and they said it depends if they have a space available for him. I am just asking if parents can choose with the placement and they want their child to go to another school where they would feel like would have better services. He has a iep in December and then end of the school year. My daughter will be going to the school I want him to go to she does not have autism but they are also close in age a year apart and I just think it would be better for both of them to attend the same school. If that’s impossible then oh well.