I just did the math Jimmy would be 4 during Siobhan's first year. Legacy takes place 12 years after the 2 wizard war ends. Jimmy is 17 in Legacy.

And Siobhan and Kyle would have been in their 7th year when Jimmy started hogwarts. 

And Mcgonagall is headmistress in Kyles universe. ...

I don't think these are taking place in the same universe.