If cops have qualified immunity that is very often used to say cops can easily get away with murder, and agents have Vance blanket twitter pardons, can they just all kill each other with no legal consequences?

Qualified immunity protects government actors from civil penalties (lawsuits) as a result of their actions while on duty and when not violating the constitutional/civil rights of citizens (that's the "qualified" part). I.e., you can't sue the cops for the damage to your doorframe after they kick your door in serving a warrant. It does not protect government actors from criminal prosecution and does not grant them license to violate existing laws, and it never has.

This is also true for ICE, which is why Vance and Stephen Miller are suddenly so keen to start screeching that they think ICE now magically has "absolute" immunity, which there is also no legal basis for whatsoever. Those pulling the strings know that ICE is in fact routinely breaking the law, and they're desperately trying to get out ahead of it while anyone believes that any shred of equal protection under the law still exists.