fedup Imo, children generally go through a stage of wanting to help, before realising it's boring/hard/novelty wears off, and then don't want to.
At 12 and 14, I absolutely would not pay them to help around the house. They wont be happy with 50p for long, honestly.
Also, I get DC's to help according to their ability, not their age, so it wouldn't bother me that 12 yr old had taken 15 minutes to empty dishwasher.
In my house for example, after dinner, no one plays/relaxes/chills out until the house is tidy...plates scraped, dishes washed (no dishwasher here), drying up/putting dishes away, wiping worktops, sweeping floor, emptying bins, mopping floor, wiping table etc and after everything has been done, either myself or DS (whoever has finished whichever bit they were doing last) makes a nice cup of tea. 
It was not so long ago that DS refused to do anything, so I empathise with you, but I had to put my foot down, and listen to him moan every single evening after dinner for at least 2 months. 
Now he is the one chivvying me along after dinner to get on with it because he knows no one sits/relaxes/chills out until it's done.