The lawyers paid to settle Prince's estate are draining his bank accounts, according to a court document filed this week by three of the late artist's heirs.

Sharon, Norrine and John Nelson, three of Prince's five half-siblings, filed a petition asking Judge Kevin Eide to review the billing practices of Fredrikson & Byron, the Minneapolis law firm that works for Comerica Bank & Trust, which was appointed administrator of Prince's estate last year.

Comerica and its legal counsel have received $5.9 million, the petition said. Comerica also gets $125,000 in monthly compensation.

Prince's estate is estimated to be worth $100 million to $300 million before taxes. In addition to the Nelsons, Prince's sister, Tyka Nelson, and half-siblings Omarr Baker and Alfred Jackson have been declared the heirs.

"There is legitimate concern that at the end of estate's administration there will be little, if anything left to pass on to the heirs," the petition said.

This isn't the first time the three Nelsons have taken issue with Comerica's handling of the estate.

Eide in December rejected a motion to remove Comerica as administrator over allegations of mismanagement of millions of dollars. Comerica billed the estate $148,540 to fight its removal as administrator.

Attorneys for the Nelsons and Comerica didn't return e-mail requests for comment Friday.

The petition asks Eide to end the monthly $125,000 payments, order that any excess amounts paid be returned to the estate and set reasonable protocols to control additional fees and expenses.

The petition said that the Nelsons tried to mediate the $125,000 monthly payment with a former state Supreme Court justice but that Comerica "didn't respond." They want Eide to order the parties into mediation so the estate's obligations can be satisfied and the administration of the estate can come to an efficient and cost-effective end.

The petition alleges that Comerica sent two highly paid attorneys to meetings or hearings with no benefit to the estate, so Comerica should pay for one of the attorneys out of its own accounts or Fredrikson & Byron shouldn't charge for duplicative time.

The Nelsons also questioned the law firm's billing practices. There are so many entries for relatively small amounts, spread over a number of different matters, that it is difficult to know if all the fees were properly incurred for the benefit of the estate, the petition said.

"Nonetheless, the huge volume of those small entries adds up to a very substantial sum of money over the period of four months," it said.

Many of the estate issues could be handled by attorneys who charge less, as the hourly rates range from $210 to $650 an hour, the petition said. If Comerica were paying for the legal services, it would insist on frugality and judicious use of more affordable attorneys, the petition said.

"If the spending on estate and attorneys' fees is not brought under control, there may be nothing left for the heirs at the end of Comerica's tenure," the petition said.

Prince was found dead April 21, 2016, at his Paisley Park estate of an accidental overdose of the painkiller fentanyl. No will has been found, so Minnesota probate law determines his heirs.