Just wanted to chime in on one small issue. My mother used to tell me all the time when I was a small child that my older sister was special and had big feelings. Her tantrums and meltdowns were unbelievable at the time. I had the same big feelings, but learned from watching how her behavior pretty much destroyed every one around her. I had my own meltdowns and tantrums alone in my room so as not to burden anyone else. My parents were so out of energy from dealing with my sister that they just didn't notice.
I categorize meltdowns as when the person's brain essentially isn't present and they just can't take anymore vs tantrums having an element of manipulation.
Her behavior always resulted in attention, positive or negative, but it also resulted in my parents choosing or avoiding situations that may have led to her having a tantrum. As a parent now, I fully understand, but as a child whose older sibling didn't want to do some of the things I liked, at the time I felt like I was being shorted. I felt at the time she was getting all of my parents energy and that life and activity choices revolved around her.
All of this is to say, be sure that the needs of your younger DS are being met. My sister and I played beautifully together, but the sibling flare ups in our family were real, even though no one paid much attention to them.
The flare ups are likely due to your daughter's age and desire to feel more grown up. Please don't discount any frustration your son might have, particularly if he has to present a false front with his friends all day.
