I’ve covered the city’s restaurants long enough to wonder why anyone would willingly enter into such a ruthless, unsparing industry. It’s filled with all the obvious problems (bureaucratic red tape, irritating customers, the constant specter of bankruptcy), and the second you look below the surface, you find it’s filled with all manner of unexpected hazards, as well. At Nom Wah Tea Parlor — which has served dim sum on Doyers Street for more than a century and has undergone a remarkable renaissance over the last decade or so — Grub Street’s Chris Crowley discovered that the business is currently imperiled by a mutual distaste among the cousins who run it. Years of simmering resentment have now boiled over into a full-blown legal battle, one that has already shredded the relatives’ relationship and now threatens their nascent restaurant empire.