Yes, it would be a good idea to set these up as one or more LLCs. Especially the one he is a part-owner of.
You can setup an LLC in most states in a day for a couple hundred dollars or less (California will charge about $800 I believe but most states it's $100-200). I paid a local company $200 and had all the documents in hand and my LLC on the secretary of state's website by the end of the day. I got a free business address to use for a year as well.
You're talking about assets worth hundreds of thousands of dollars. So it would definitely be worth spending a couple thousand dollars to consult with a CPA or attorney on setting these up properly, especially the one with his brother. It can be done on the cheap by yourself, but for that kind of money, it's worth it to get professional advice.
From a tax perspective, nothing will really change. Any income or expenses from these businesses will flow through to your personal tax return and be entered on a Schedule C, maybe a Schedule F (not sure how the IRS looks at leased out farmland vs. operating the farm yourself). For the one with his brother, the IRS treats it like a partnership and each partner is responsible for their portion of the taxes. So if they're 50-50 owners, and the profit is $50,000, each will have $25,000 of taxable income. But, the IRS can come after either partner for the whole business. I've heard of minority investors getting stuck with the tax bill for a whole business when the majority partners run off (perhaps after embezzling all the assets from the business). Hopefully not a concern amongst family. But, that's why a good partnership/LLC Operating agreement are critical.
