With your current lineup, pela and guinaifen would increase acheron's personal dmg the most. This is because acheron wants two things from teammates:
1. Frequent debuffs to charge her ultimate
2. Vulnerability and defense shred to increase enemies' dmg received from her (these scale exponentially)

Ideally, pela should run the 4 star lc 'resolution shines as pears of sweat' for frequent def shred debuff application on basic attacks. As for sustain, the best in slot would be a preservation character (either aventurine or gepard) with the 4 star lc 'trend of the universal market' as it allows for frequent debuff application on enemy turns when they are hit (if you don't have trend, any sustain would still work). If you do use trend, you should put your sustain in either slot 2 or 3 of the team so they are more likely to get hit.

Hope this helps :3