I think the deal is that the mortal and the immortal have different values. (non-immunes and immunes)
You hit a mortal target that got killed, only to be healed by a doctor which then were killed. Technically only one was killed - but you did indeed kill two targets in a row.
The immortal wouldn't be killed or injured so that wouldn't count. (If I get that correctly)
Since it's a mass murderer that visits the house of someone, shouldn't
everyone die?
The OoO of doctor is after kills, but doctor remains killed so I wouldn't see the direct logic since an alive person would "still" be visiting.
MM is confusing and I think it needs some clarification regarding just a few things.