Aspiring songstress Alli Simms, the first cousin and former assistant of Britney Spears, has been subpeoned to testify in the custody war waged by Brit’s ex Kevin Federline.

Kevin’s lawyer, Mark Vincent Kaplan had Alli served at 3 a.m. this morning. Alli was at an LA house party, and was “absolutely angry” about what was happening, says an eyewitness.

Alli will be questioned about cuzo’s parenting skills – including whether she changes diapers, and whether the mom of two drinks too much.