How to recover data from crashed nas?

Hi – I am in a bit of a sticky situation and am hoping someone can help me out. I have a 4 bay DS418Play NAS with all 4 bays in use. I had set it up as SHR1 but after one of my drives crashed, I replaced with a new one. However soon after that, the new drive crashed as well. I figured my NAS is falling apart and i need to buy a new one, so i shut the NAS down while waiting to buy a new NAS. 2 days later, i needed access to a file urgently on my NAS so i turned it on and downloaded my file, but my NAS suddenly restarted and after restart I had another drive showing up as crashed. So now I have 2 drives crashed out of 4… and after the restart when I tried to access my data in the NAS, i could not see any data in the NAS 🙁. But i feel certain that the data is not lost in the drives and it is the NAS which has caused the drives to crash. But i am not sure how to recover my data safely. I have not turned on my NAS since that day yet. How can i recover my data or rebuild the NAS (or transfer to a new NAS) with minimal risk of loss of data? I would like to avoid giving my drives to someone else (e.g. a professional) if possible for privacy reasons.