Remember, you are the pulse of your ministry. If your staff sees you putting in the time and taking your job seriously, they will do the same. If they have all the material... they are the ones responsible now. Wow! That's right. Transfer responsibility and you will create an expectation of them. They will not come unprepared because you have set them up for success. Now if they fail, it is on them (well, it is still on you – but you catch my drift). They will do crazy stuff like bring your lessons and group questions all marked up with ideas they have for their group, ideas of stuff specifically for their students and ways they can be a better leader.
Also, they will come with questions for you about the passages you have chosen for the next few months, which makes you be accountable for the stuff that you put out. And we all know that it is nice to not have to have anything in writing so we do not have to answer. However, that is not good ministry. Good ministry is getting your material out on time. So, even though you may behind the curve already for this year, you still have time to get on it. Put in the extra time. Put in the long hours now and you will thank yourself later on this year when you are coming up to the holiday season and you are ahead of where you have ever been.
Setting your staff up for success will put you way beyond where you could get the group on your own talents and skills. So, get them as much material and calendar items as quickly as you can. The more they have the more success you will give them and will build confidence as a team. They deserve the chance to do the best they can with the students God has put in their groups. And you will stay sane... at least for a long period of time.