Wow, this second post is a very positive post.  After reading your initial post, and all the other replies, and then your second post, it seems very positive.  The fact that your hubby's sister is encouraging the parents to start making plans is a very good sign.  And the fact that your hubby's parents are willing to do this is a very good sign.

I'll make the following comments:

a) you need to work on the things that you have control over.  Right now, you may have very little input into the farm's finances; however, you have your own personal/ family finances.  You need to make sure you are managing them well - create your own family budget so you know what is coming in, what is going out, and where it is going to.  Having these skills in place is going to help you if and when the time comes for you to be more involved in the farm's finances.

b) make sure you are working on your marriage. You and your hubby need to be on the same page.  IF you aren't, the farm won't matter.  (and after reading your second post, I think you are on the right track here.)

c) start thinking about how you can fit into the farm. Maybe you can't do a lot of the physical aspects of the farm.  However, the farm's finances and marketing are important aspects.  If that is something you can learn, and eventually contribute,  go for it. 

Lastly, you - and your hubby - probably need to remember that just because your in-laws ran their farm a certain way, does not mean that is the way you and your hubby will need to do it.  Your and your hubby need to decide - together - what is going to work in your marriage, and what is going to work for the farm. 

Good luck.