Omaha’s NorthStar family of financial services companies has agreed to sell a majority stake to a Boston-based private equity firm. TA Associates, whose investments include Omaha data center operator Cosentry, said Monday it has agreed to buy a majority share of NorthStar Financial Services Group. NorthStar operates nine subsidiary companies that serve advisers in the wealth management industry. The companies said in a statement that NorthStar executives will continue in their positions and will continue to own a large stake in the company. Financial terms were not disclosed.