In the class I am mentoring, I have three students who I have to work with everyday after school. Two out of three of my mentees are best friends and are constantly talking in their native language. I have tried seating them farther from one another when we all work together, or having me or the third student sit between them. The teacher of the class knows they talk a lot, but only tells me to address it myself.
Right. You need the let the student know you are the authority figure.
Consequences do seem like the next possible solution to this issue.
This could work. But make sure to have a backup of some sort in case it doesn't.
They may be speaking their native language to help them with the work, asking them to speak English only is not respectful of their language.