can I have two separate iPhones linked to the same iCloud but running on two different iCloud backups?

So I can’t get my second phone to use a backup that’s on my first phone is what you’re telling me?

No. You can restore a newer device using a backup from an older device.

I am trying to make my second phone reset to a backup from a year ago while having my main phone work as it is now.

That won't be possible. If you had an iCloud backup of a device and you stopped backing up the device, the backup would be deleted after 180 days. iCloud backups are incremental and always backup the current state of the device. Eg. old backups do not exist.

You can use any older backup to restore to a device running the same or newer iOS. You would not need a new phone if that is the case.

But, you still will not have any backup in iCloud that is more than 180 days old. And, if you were continuing to backup the device, it will only have the items that were on the device as of the most recent backup. So, if you stopped backing up your old phone, and it has been more than 180 days since the last backup, no backup exists. If you were backing up your old phone, then the only backup will be the one that you most recently made.

Your devices back up independently of each other. So two devices will each have their own backup to iCloud.

iCloud keeps only one backup per device.