Those are two different scenarios so no reconciliation is needed. Luke 19:50 is talking about somebody doing things in Jesus’ name and Matthew 12:30 is for that who actively oppose or reject Jesus Himself.
...Matthew 12:30 is for that who actively oppose or reject Jesus Himself.
In essence, one says those that are not actively agianst Me are still against Me. And the other says those that are not actively against you are for you.
To paraphrase further. It’s as though one says that if you are not actively against me, you are for me, and the other says if you are not actively for me, you are against me. i.e. one tells the guys in the middle they are against Him and the other tells them they are with Him.