I did that for a couple years...busted my rear end and flat out wore myself out... told my parents I'm not doing that again and we figured up every job on the farm priced at custom rates. if I want to pick up more work I pick it up at what it costs them to custom it out. If I am doing a job and I can't do it all I can hire it out. Its my responsibility if I take on the job. It keeps things separate and fair. You don't feel guilty about you not doing something because you or they hired it out. 

Your income does drop as your working less. but you also get to spend time with your family knowing that things are still getting done. and if you have bought a machine yourself and you are working for your parents and they are paying you custom rates then you are free to pick up custom work at others farms as well... If everything is hired out instead of hourly then all the work gets done and your left deciding what work you want are capable of doing timely...

only thing I get paid by the hour anymore (truly an employee) is during harvest. then I'm on their hours but that works out pretty well... 

good luck. do something now... you only go around about this life once.