Michael Lockwood has formally asked the court to appoint him as guardian ad litem so he can represent his twin daughters' interest in Lisa Marie Presley's trust battle.According to legal docs, obtained by ET, Lockwood filed the legal documents in Los Angeles County Superior Court on Thursday and said he should be appointed as the guardian to represent 14-year-old twin daughters Harper Vivienne Ann Lockwood and Finley Aaron Love Lockwood in an upcoming hearing in probate court, which is slated for April 13.In the documents, Lockwood notes he wants to officially be appointed as the twins' guardian because «the minor is a beneficiary of a trust at issue before the probate court in the above-referenced case. The minor requires appointment of a guardian ad litem to represent her interests in the proceeding.»He added, «There is no conflict regarding appointment because the proposed guardian is not a beneficiary of the trust instrument at issue.»Harper and Finely each signed the form consenting to Lockwood being their guardian.This is the latest development in Lisa Marie's ongoing trust battle.