Have your characters train Social, Connections and Negotiation skills to at least level 4. That will help a lot with the standings grind. If your main concern is only to have your other characters gain access to that one specific level 5 agent, then what the other players have posted above should do just fine.
Believe it or not - A character with high Faction standing will have access to all Agents of all Corporations within that specific Faction.
The quickest way to accomplish that is by completing missions for Event_Agents
. Each mission gives a Faction standing increase and gives player characters a very large kick start for accessing high level agents.
Of course each character will have to get the mission offer separately but if needed, can have others help complete it, then turn in mission as completed by single player, not as fleet.
You don't necessarily have to complete all of the Agent missions listed in that link, just completing the majority of those missions will give a substantial increase to Faction standing. If all members of the Player Corporation have high Faction standing, that will help increase the Player Corporation standing to allow anchoring a POS in Empire high security systems if so desired.NPC_Faction_standings_towards_Player_corporations
I've listed a lot of guide links in my Faction Standing Repair Plan
which can also be used to increase positive Faction standings as well as repair negative Faction standings.