1. RAID Controller issue
2. Multiple drive failure
3. Corrupt file system
Those are a few. If you value your data, you should get a full sector-by-sector clone of each drive before you try anything further. At this point, the chances of recovery are high, and cheap, but I simple mistake could make it a very low odds recovery at a much higher price.
Once you have the drives cloned, use a software program like R-Studio or UFSExplorer to virtually reconstruct the RAID array, recover the file system and copy the files out to a new device/RAID array. Make sure you set the original drives aside, just in case you do decide to seek professional data recovery assistance. They will likely need to work from the original drives as they are at the time of failure.
I'd be willing to help you out remotely, if you wish...preferably with clones.
Edit: this offer for remote support is intended to be free assistance and is not an attempt to sell my services