XFS drives can only be single member pools. This is not a bad thing in my opinion, considering the next best option for differing drive size pool use is single profile BTRFS pool, which gives you the sum of the member sizes at the expense of losing everything on both drives if one fails.
You can't add the 4TB to the 1TB existing pool as XFS.
What you would do is set up another pool, not add it, and call it vms2_nvme.
I'm not sure if that's what you were trying to say, but if you have 4 total SSD I would recommend each having their own named pool, not combining them. The only time I personally would combine multiple drives in a single pool is if they were identical and I was using the mirror (RAID1) function of ZFS or BTRFS. I don't particularly like BTRFS though.