I am not a fan of having to rescue the senators first. Its going make our negotiating with the unions incredibly awkward/difficult.
Doing it at the same time makes us look even worse. It would make us look underhanded.
But I suppose we have to do what we have to do.
Our plan is going to be dependent on the senators and their location/situation. But it should be a quick, in and out, no killing type of deal. Mind tricking and stuff like that.
Do we have any idea where they are being held?
OK, so then the goal is going to be. Get onto the ship, and make an escape.
Do we know if they have any sort of anti-air defenses? They are a kinda backwater planet right? If they don't have any defenses, we can just fly the ship away. We do have to overtake the guards and things, but we should be able to that non-lethally, or through diplomacy. Hopefully diplomacy.
So my suggestion for a plan is this:
We land as close to their ships as we can, while remaining hidden. We attempt to get onboard the senators ship without being seen, we then free the senators, and escape in their ship. Then from orbit, we contact the union, and offer to talk. If we can figure out a way to get dropped off, rather than land our ships it would be best. That way we could transfer back onto our own ships and let the senators head back while we stick around and talk to the unions.
Why not simply liberate the senators and put them under our guard? Are we specifically supposed to extricate them, or can they stay to do their job once we free them and settle things down a bit? Otherwise we'll have to work to temporarily neutralize the local air defenses.
The rescue will effective annouce our arrival, and our doing it sans bloodshed will signal that we are here to enfore the laws, and are ready to negotiate. Jedi style, beginning to end.