RAID1 Recovery after Degradation

It seems both of your disks are dying:

/dev/sda:
  4 Start_Stop_Count        0x0032   096   096   020    Old_age   Always       -       5039
  5 Reallocated_Sector_Ct   0x0033   100   100   036    Pre-fail  Always       -       240
187 Reported_Uncorrect      0x0032   079   079   000    Old_age   Always       -       21
195 Hardware_ECC_Recovered  0x001a   044   015   000    Old_age   Always       -       26908616

/dev/sdb:
  4 Start_Stop_Count        0x0012   099   099   000    Old_age   Always       -       4911
  5 Reallocated_Sector_Ct   0x0033   088   088   005    Pre-fail  Always       -       90
196 Reallocated_Event_Count 0x0032   100   100   000    Old_age   Always       -       114
197 Current_Pending_Sector  0x0022   001   001   000    Old_age   Always       -       9640

So, again, never trust to what it says about itself, it lies!

You need to connect a third disk, partition it and add it into your RAIDs. Wait until it finishes rebuild. Intstall bootloader there. Then remove those two failed, and connect fourth one and replicate again to restore redundancy.

And setup periodic check and monitoring, to avoid such a dangerous situation in the future.

It is surprising to see separate boot RAID array with LVM on it. Very unusual. The original purpose of separate boot partition is to not to put it inside LVM so it could be accessed easier (early bootloaders did not know nothing about LVM, so that was a requirement).