Sort of, but it sounds like you are thinking the parity disk is more important than it actually is. Rebuilding a disk requires all the other drives to be healthy, so if disk 1 isn't healthy, the rebuild of both disks will have corrupt areas where disk 1 was unable to be read correctly. This very likely will result in unmountable file systems on both disks, which may or may not be recoverable depending on where the corruption is.
Unraid will fail the rebuild of disk4 as soon as it encounters an unreadable sector on disk1. So, the only way forward with any chance of success that I can think of is to use ddrescue to clone disk1 to a healthy drive of the same exact size. This will allow Unraid to read all the sectors, even if the data there isn't accurate, so at least the rebuild of disk4 can complete, albeit with data corruption in the areas that failed the read during the clone process.
It would be much better to simply recover the data from your backups.