If my boyfriend was in an at-fault wreck in a work vehicle and is now being sued along with truck’s owner and insurance company, what do we do?

Typically, in lawsuits like this, liability is "joint and several"--that means that theoretically, each party sued could be held liable for the full amount. (Note: the insurance company is not really being sued separately; it's responsibility is to pay for their insured, to the limits of the policy, if their insured has to pay.)

The court does not "decide" who pays what share in this case; it's up to the winning plaintiff to decidee who to go after, once a judgment is in hand, to actually get the money, though multiple defendants may agree among themselves how to share costs. Usually, the plaintiff goes after whomever has the money, though may go after any defendant.

For example: say the plaintiff wins $250,000 and the farm had $100,000 insurance and could otherwise pay (based on assets and cash flow) another $100,000. In that case, the plaintiff could get $100k from the insurance; could hope to get another $100k from the farm; but then if the farm had nothing more to give, could try to get the last $50k from your boyfriend. Generally again, plaintiff's name everyone to have as many options to collect as possible, but focus on defendants with "deep pockets."

If your boyfriend does  have to pay something but doesn't have any money, the plaintiff can try to put a lien on property--but he doesn't have any--or garnish income--but there isn't any. In short, as a practical matter, regardless of the verdict, the plaintiff might not be able to collect from him--can't get blood from a stone, after all.

However, a judgment against someone hangs around for years, and the plaintiff could try to enforce it later, if your boyfriend gets into a better financial position. If there is a judgment against him, your boyfriend may wish to consider bankrupty to eliminate it.