After you accepted a bad answer, I am really sorry for my heretic opinion (which saved such arrays multiple times already).
Your second failed disk has probably a minor problem, maybe a block failure. This is the cause, why the bad sync tool of your bad raid5 firmware crashed on it.
You could easily make a sector-level copy with a lowlevel disk cloning tool (for example, gddrescue is probably very useful), and use this disk as your new disk3. In this case, your array survived with a minor data corruption.
I am sorry, probably it is too late, because the essence of the orthodox answer in this case: “multiple failure in a raid5, here is the apocalypse!”
If you want very good, redundant raid, use software raid in linux. For example, its raid superblock data layout is public and documented… I am really sorry, for my this another heretic opinion.