Getting shot is a occupational hazard of being a burglar.

As far as overkill goes, if the burglar is still moving and trying to get up then they are still a threat and you need to keep shooting to eliminate the threat.

What else would you do? Stop firing and wait for them to pull out a gun and shoot you or throw a knife at you? Run away and get caught by their accomplice outside?

Unfortunately, one must assume that anyone breaking into their home means them harm. Failure to effectively counter that intent is suicidal. It is not nice, it is not kind and is very unpleasant to contemplate but the intruder is the one who made the choice. Deal with it or suffer the consequences.