For question 4 it’s les because it’s plural considering ellas is a group of girls. question 5 is nos because the pronoun is nosotros meaning “we” hope this helps.
I was taught to call them yo -go irregulars because the verb's stem ends with -go in the yo (I) form
Ex: Yo Tener(To have) becomes "Tengo"
Yo Venir(To come) becomes "Vengo"
Hope this helps
