Yes, it's common. But, common or uncommon, if it was agreed to, then it's binding, absent proof of some conscience-shocking unfairness.
However, it's not clear to me how the two individuals' making a personal guarantee for the loan, makes the rest of the owners personally liable. It just makes the company liable. So, unless you are one of those two "guys," I don't understand the concern. Maybe you can clarify for me.
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