I would say "los quiero" but if the people (plural) that you're referring to are females and only females then you'd say "las amo". I've been taught Latin American Spanish. My guess is that in European Spanish, they'd probably say "os quiero". Both are based on plural forms of tú (which in Latin America is ustedes but vosotros(as) in Spain).

En España se dice "Os quiero".

se dice (Los/las amo)