Dean's eyes narrowed. He was slightly torn - protect Seamus's mum or fight this woman. He watched as his second mum sat down, that glazed look in her eyes and reached for the bottle...but after only one long cut, she made it perfect clear that she was, in fact, a woman of extremely great strength of will. As Dean saw her struggle to come out of the Imperius, he relaxed slightly turned his attention on the woman.
"It doesn't matter how I know you. I know you and I know you've been killing people. You won't be killing us." Dean whipped his wand, casting a powerful diffindo charm, a severing charm, at the woman in question. She'd already cast an unforgivable curse. He was not holding back.
Behind him, Seamus's mum tossed the bottle away and drew her own wand, her eyes flashing. From her mouth came a string of cursing - again, not hard to see where Seamus got in from - before she cast her own spell - incarcerous.