S.W.
Don't explain the last 18 months at all on your resume. A resume is to show the accomplishments you've had in your field, and your skills and education.
For an interview, prepare a one sentence response to any question about what you've done for the last 18 months. Do not apologize a bit and do not say that you are back in the job search because your husband lost his job. "I took time to be at home for family reasons but I am now ready and excited to be back in a professional position and contributing to an organization."
Most interviews will require formal business attire even if the office is normally business casual. I go to interviews in a black pant-suit with a nice blouse and shined shoes, restrained jewelry. Business casual means you can take off the jacket or substitute a sweater, and maybe be a little more creative with shoes/ boots and jewelry and accessories. Different companies have different expectations when it comes to business casual, so I wouldn't do much shopping before you land a position and see what others are wearing.