Hi there,
Thank you for reaching out. You can achieve this by creating a document of 8.5 x 11 and copy-paste your artwork from these two 5 x 7 artboards. Also, you can simply create an 11 x 8.5 artboard in landscape and copy-paste your artwork from those two artboards and print.
Let us know if you need any further assistance. We'd be happy to help.
Thanks & Regards,
Anshul Saini