My father in law is Moroccan and has a Spanish residence card. My wife and I live in London. Can he visit us without a visa ? Or does he need to apply?
Your father-in-law needs a visa based on his citizenship https://www.gov.uk/check-uk-visa/y
If he is an Article 10 residence card holder he may use that document for travel to the UK if he is accompanying his EEA national relative to the UK, or joining his EEA national relative in the UK. https://www.gov.uk/government/publications/entering-the-uk-as-the-holder-of-an-article-10-residence-card/entering-the-uk-as-the-holder-of-an-article-10-residence-card