A group of hedge funds and investment firms that hold debt insured by a business of Ambac Financial Group Inc. sought in court Monday to stop cash from flowing out of the beleaguered bond insurer to its parent. The plaintiffs, including Aurelius Capital Management LP, Fir Tree Inc., King Street Capital LP, Monarch Alternative Capital LP and Stonehill Capital Management LLC, hold more than $1 billion in mortgage securities or other debt insured by Ambac Assurance Corp.