Infighting and tax troubles threaten the future of a citizens’ group founded to improve the Summerhill community near Turner Field. The Summerhill Neighborhood Development Corp. has sued its founder, former state Rep. Douglas Dean, alleging he secretly pledged the nonprofit’s property to back $2.4 million in bank loans — now in default — to benefit a private developer. The non-profit, according to the suit, “now faces the very real possibility of losing substantially all of its real property assets.” In addition, federal tax records list $470,000 in unsecured, interest-free loans from the non-profit to Dean and his wife, and $50,000 to the group’s new CEO. Dean says those payments were reimbursements of money he loaned the non-profit over the years. IRS auditors could find little or no documentation for those debts.