Nephew Insisting on Bringing Girlfriend to Student's Birthday Party

My (32M) nephew, "Thomas" (18M), is friends with one of my students, "Jodie" (16F). Thomas attends the same high school where Jodie's mother (41F) is a teacher. These are all aliases, not their real names.

Jodie is planning to celebrate her seventeenth birthday early since she will be away on her actual birthday. The issue is that Thomas is insisting on bringing his girlfriend, "Becky" (18F), to Jodie's party. Jodie has never met Becky and doesn't want someone she doesn't know at her birthday celebration. She is not romantically interested in Thomas at all; she simply prefers not to have strangers at her house for her party.

My brother (40M), Thomas's father, agrees that Becky should not come if Jodie doesn't know her and doesn't want her there. I also agree with this.

I'm wondering if anyone has advice on how to best handle this situation within the family.