When the host said the announcement, it was very clear that you were in the same dormitory, and one dormitory was willing to go on stage together, showing a very good friendship.
So I think the stage effect is what you should think of, because you may want to show the friendship between brothers and let the audience give you better evaluation and more applause.
I suggest you join the dance. Dancing together can highlight your unity and tacit understanding. You can choose some simple actions, similar to military training, which can also be found online. Simple movements will not affect singing.
If you have knowledge of music, you can choose a high school bass trio, which is more powerful, but it may be more difficult. You can ask a music teacher for guidance.
If you can sing for a long time, you can also add poetry reading, which is also the simplest.
There is a simpler one, that is, clothing! With the combination of clothing and singing, you can choose uniform and exaggerated clothing, which can be very pure and can also highlight everyone's personality, but it must be different from ordinary clothing. After all, now you are performing, and on the stage, you are the protagonist.