It's not normal, but not unheard of either, there are as many different stories as there are posters on this board.  Don't worry about being insensitive,, long as you're straight forward,, and confused people will ask enough questions to gain a better understanding.

I realize I'm only getting 1/2 of the story so it is only worth what you're paying for it.

Father in Law is "controlling" to the point of being a detriment. Mother in Law isn't firing on all cylinders complaining you can't do the manual farm labor,, yet,, conviently forgets your paycheck is apparently what puts food on the table since for whatever reason the "In-Laws" don't pay Hubby for working full time. 

You didn't say how old you and Hubby is, or how many acres in farm? or Location, or crops grown, etc. (hard to offer ideas without some knowledge of total farm capability-capacity.)

Where does your Husband see himself in 5 years, 10 years, 15 years ??  What are his plans for the future, both of your futures ??  

If you don't know the business of the farm,, how do you know there's no "net gain" ?   Is that just what your FIL says ??  What is your Hubby's education ??

Honestly,, it sounds like the FIL isn't too sharp about "how" to make money.  (let me guess every penny spent he sees as "spending" the word "investment" doesn't even equate in his mind ??)  A further guess is,, FIL is counting the pennies and the dollars are and have been floating away for years. ( I've got personal knowledge about that aspect!)

Far as "learning about farm business"....  There is a pletora of information on the internet about Farm business.  Stick with "EDU" for a domain when looking for say,,, "ag budgets" and you will get plenty of information.  Marketing can be handled the same way. Ag colleges have a LOT of information available.  You can learn the "business" and there is NO, I repeat NO substitute for being an astute Farm Business manager.  Millions of dollars in equipment, or fancy pickups, or "whatever" is not a direct corralation to being a good Manager. (If you understand what I mean?)   Has to be efficient, Has to make money over and above the investment capital, and labor, etc, (ROI)

Debt has to be handled "correctly"  It is an invaluable tool,, but,, it can also turn into an axe and cut your head off if used Improperly.

The only thing nobody can help you with is your Hubby "standing up to his Dad".  He is going to have to do that ALL on his own.  You can't help him or do it for him, he has GOT to find the "stones" to stand up and fight for his and your Futures,,, IF he want's it bad enough  ??

A wild a$$ guess,, but I am guessing the "family farm" has Z.E.R.O  long range Planing for your FIL and MIL dying, and/or where they cannot fend for themselves any longer. 

For some stupid reason,, some people in their 70's think they are going to live forever,, or,, somehow mystically the farm will be passed on to the offspring.  Wrong, way wrong, completely wrong.  FIL and MIL are going to have to pull their heads out of the sand (or wherever) and realize they are not going to live "forever" and IF they really want your Hubby to continue the business they are going to HAVE to make some radical changes PDQ.

(I know,  I buried both parents who thought they would live forever..)

Don't get overly wrapped up about the "size" of the farm. Probably 80% of the posters on here are "dryland farmers" they do not irrigate. (plays a huge role in what a farm is capable of)  Some do irrigate and have to just to get a crop. (myself for example) 

There are "big farmers",, (you'll hear "BTO" big time operator, "STO" small time operator, and everything in between.  Again,, it's about being sucessful and feeling sucessful, and most importantly being financially sucessful.) 

You will get a lot of suggestions, just about bet #1 is going to be your Husband deciding what he wants to do, then standing up to his Dad and making his points.   All I can say is, LIfe is short, if your husband is adult enough to ask you to get married, he is adult enough to STAND UP to his Father.  I am not trying to be mean or hurtful, your Husband is going to have to make his intentions known to the FIL, and he is going to have to decide what he want's from life for both of You.  Think of it this way,, What happens if FIL-MIL gets in car wreck next week and they both die.......   What is your Husband going to do then ??? 

 IT is Said,, "life is what you make it"...   my question is,, what Life are your Husband and You making for yourselves  ???

I realize I've bounced all over the issue (s) and appologize for that.  I was just typing down what came to mind as the thoughts flowed.