Do you actally have two disks that show up as xvda1 and xvda2? I'd have expected xvda and xvdb.
Also, assuming you have two disks, xvda1 and xvda2 (instead of xvda and xvdb) I believe you just need one clearpart line:
clearpart --all --initlabel
At the very least, I think you can combine the two:
clearpart --all --initlabel --drives=xvda1,xvda2
I'd try switching xvda1 to xvda and xvda2 to xvdb first unless you know that you've got two disks with those device names. If you do, then you may try looking through the fedora kickstart guide: