Hi supportit4,
This link works really good, in this case considering you only control the ASA 5516 you can check the config of the FW2 on the following link:
https://networkology.net/2013/03/08/site-to-site-vpn-with-dual-isp-for-backup-redundancy/
From AWS perspective they should configure the tunnel pointing to both of your interfaces and if the primary goes down use the secondary.
Hope this info helps!!
Rate if helps you!
-JP-