I love it!
Jasper and
Jemima sound awesome together. I don't mind same-letter siblings as long as it's not too matchy (like
James and
Jemima, or
Adam and
Adeline).
I used to love
Jemima, but I always get negative comments about "Aunt
Jemima", so I'm not sure it's usable in the US. Since you're in Australia, you should definitely use it. I would be sooo happy if you ever used
Jemima!