If you still need this achievement before the servers close, and you don't have enough players on the same team for a chemistry, there's a much easier way that involves a small amount of luck.
Get your Ultimate Trainers boosted players from the challenges first, that'll get you the first chemistry set without trying. Now if you don't have enough players on the same team with their team's logo on the side of the card (that's the chemistry icon), then we're going to look through our Item Binder to pick out players that can be upgraded.
Only players that are Gold or above can be upgraded. Identify how many players are on offense and defense that can be upgraded, and whichever side has more is the side we're going to aim to upgrade 5 players for.
Go to the Store, go to "Get More Packs," then scroll to the right for "Get a Player" for 500 coins. You're going to keep buying these packs until you have 5 upgradable players on
either offense or defense, in 5 different positions.
Once you have them, go to "Adjust Lineup" and make them all the starters in their own positions. Hovering over a player, hit
, then Upgrade. It's going to cost 25 Training points to get this achievement, so if you need more, quicksell some players that aren't in your lineup. Once the player is upgraded, equip the "Balanced O" or "Balanced D" in the only chemistry slot.
Repeat for the remaining 4 players and the achievement should pop. If it doesn't, swap out one of your upgraded players and swap them back in, because I had to do that for mine to pop. Hope this helps.