Was it illegal to open two accounts between me and my husband?
It's against their TOS most probably, because how would they know whether it's different people creating those accounts if IP address is the same?
I will provide all the documents required but I would like to know first if what we did was prohibited or not.
What you did is prohibited in every platform, you can't create multiple accounts using the same IP address, if you do, you will either get banned or restricted and then asked for identity verification.