Answer:
Las
Step-by-step explanation:
"Las" would make the most sense because the people Ernesto is referring to are all "sisters (hermanas)" aka all women
Whenever there is a group of women being pointed out, you have to use the feminine term for "them" which is "Las"
"Los" would work only if there was a male or males among them or only a group of males in general
"Lo" and "La" are singular but "hermanas" is more than one sister therefore those would be incorrect also