Comment by tamagoshiii on Jujutsu Kaisen - Chapter 162

If only one of them is lying, my bet is that would be Amai. Remi is introduced as a sly girl, while Amai is introduced as a character that is somewhat "familiar" with yuji (same hometown). 

Remi's attitude seems suspicious, but given the situation they are in, what she's saying makes sense. Which in itself, could be a genuine response.

Meanwhile, Amai may seem safe because he is introduced as someone who already knows yuji and is from the same town, like the familiarity wants to make us feel at ease, but remember, he already ditched the two people he was cooperating with.

I could be wrong tho. Just a hunch.