im in a similar situation, im 21 and coach our junior team but cheer on the senior (senior isnt capped in the uk you can be as old as you want). We had a couple of lazy people my age but they were in my stunt group so i made them work but there was one backspot from the group next to me who had the WORST attitude! came into cheer with a hangover, didnt want to stunt, wanted a different flyer, moaned every time she caught her flyer... well one day i'd had enough (i didnt necessarily mean to do this it just kind of happened) i turned and just plain out yelled at her that - she was lucky to be in our team, she was lucky her parents paid all her tuition, she has one of the hardest working flyers in our whole program!! Hangovers are no excuses because she chose to drink and she chose to go out clubbing, it should never be taken out on the team.... her reply to this was "if you keep this up i will just quit" ... my answer was the door is there don't let it hit you on the way out.
she was so shocked that i was happy for her to just leave that she actually sat in tears while i explained without her negativity the team would be a) happier and b) more productive. Well she is never said a word for the rest of that practice , we only had a couple of weeks left of the season and she didnt moan. BUT now she is back with a totally different attitude!
If you are a coach and have a bit of authority maybe try explaining exactly what their lazyness is doing to your team and if they are adults they SHOULD understand