Ultra Instinct Goku is faster, stronger, and more agile compared to his opponent and on top of that, there is a significant difference in their respective power levels. By the time Broly increases his power level, Goku might have found an even greater control over Ultra Instinct.
No. He’s too mentally unbalanced. And if that was not enough, because he instinctively accesses his Oozaru power without transforming, that power also helps his mind to become even more unstable. And remember that Ultra Instinct is such a deep state of mind that has to leave all emotions aside, and move beyond them.