The Lamplighters League

Quick and simple way to get this done (and the other Agent achievements) without needing to recruit agents.

--Main Menu--
Step 1 - Create new campaign
Step 2 - Choose "CUSTOM" game option

--Custom Game Options--
Step 3 - Turn off the tutorial missions (skips us to Week 4)
Step 4 - Choose the Agents to start with on the custom game option list

Choose a mission and beat it with the selected crew. Done - easy.

--List of Crew Achievements--
- Fedir & Purnima
- Fedir & Juidth
- Fedir & Ingrid
- Celest & Ana Sofia
- Lateef & Judith
- Ana Sofia & Jianya
- Celest and Alex

Like all of the achievements that require you to complete a mission with two specific characters, you don't actually have to duo the mission, you can bring a full team of three or four (in those missions that allow four agents, specifically the three final missions of the three heists, the keystone missions and the last stand mission, which pops up when one of the house clocks reaches 40 as a last chance to stop them from winning and knock them back to their last escalation threshold).

Célestine and the Alexandrite are probably the most difficult of those team achievements, because they both have very gimmicky kits and don't deal much damage. They have great synergy for causing stress, which makes them good against strong tanky enemies that come in low numbers, but they are weak against big crowds of average Joes.

The easiest way to do this is to take them on a mission for four agents alongside a fully built Eddy with a storm card for maximum action point farming (He can deliver A LOT of medium damage bullets in a single round, getting up to 5 bonus action points, which helps to both deal with swarms of weak enemies as well as pushing the strong enemies that are affected by Celestine and Alexandrits stress spells over the edge) and either the Chinese sword fighter or Ingrid to zoom around the battlefield and knock the stressed enemies out.