Ask them to leave with a Speech check or NCR fame check.
Ask Marcus to pay the mercenaries to leave.
Reward: NCR infamy
Reward: 350 XP without asking for money
Reward: 250 XP and 2500-3000 caps (gives Bad Karma for 3000 caps)
The second time one visits Jacobstown, Marcus will approach with news of New California Republicmercenaries harassing the town. He will then ask the player character to peacefully deal with them. When asked why the mutants don't kill them, Marcus says it is to avoid giving the NCR an excuse to exterminate Jacobstown.
To resolve the quest, the Courier can return to the entrance of Jacobstown and approach the mercenaries. They have the choice to pay them 2500 caps or tell them to leave with a Speech check of 65. If the player character has a very high NCR standing they may also be able to tell them that they are an NCR hero, upon which their leader Norton will recognize the player character and they'll leave. If the Courier doesn't have 2500 caps, they can talk to Marcus who can be asked for 2000, 2500, or 3000 caps to pay off Norton and his mercenaries (requesting 3000 results in negative Karma).
Alternatively, the player character can also kill them, but this leads to a lower XP reward and lowered reputation with the NCR. After completing the quest the player character will gain 350 XP, or 250 XP if they asked for caps from Marcus, regardless of whether they used a Speech check or gave the caps to Norton.
Speak with the leader of the mercenaries harassing Jacobstown.
Come to a peaceful arrangement with the mercenaries.
The mercenaries can be quietly killed while on their way to the campfire without incurring NCR infamy.
It is possible to keep the caps given by Marcus without paying them to the mercs. First, ask Norton about by what means will they go away, then go to Marcus to ask for caps, return to Norton and pass the speech check or NCR reputation check, finish the quest after reporting to Marcus. By the end, one should have earned 250xp and 2500/3000 caps. In addition, the Courier would not earn negative karma for "cheating" Marcus. However, they still receive negative karma if they ask for 3000 caps instead of 2500.
After convincing Norton to walk away via caps, the area just south of Silver Peak Mine shows a non-hostile non-player character on the compass. The spot the compass points to shows an option to talk to Norton and one or more mercenaries. Doing so does not activate a dialogue. [verified]