Gary Anderson (25) and Sean Anderson (23) both of Grafton Street in Derry had denied the murder of Karol Kelly on March 4 2018.
Both face life imprisonment after being found guilty by a jury.
A third defendant Michael Dunlop (21) of Fern Park in Derry was found not guilty of the murder but guilty of attempting to inflict GBH on Mr Kelly.
Following the verdict, Judge Philip Babington told the Andersons that there was only one sentence he could impose and that was one of life imprisonment.
He said at a later date he would set a tariff to determine how long they will serve and for that he would seek reports.
He set a date for September 9 to do that.