BLOOD may be thicker than water, but for the Tang clans' blood may soon be about to boil in a dispute over land ownership. Descendants of two Chinese patriarchs who were members of the same clan are claiming ownership of five lots of land which they jointly owned with two other Tang clans. At stake is 68,000 square feet of remote hilly land in Tai Po which the heads of the three clans bought in 1928, each paying $5,000. Two of the clans are united in their wish to sell the land, but members of the third are bitterly divided over which of them has the rights to the property and the title deeds. With the issue of a Supreme Court writ last week it looks as if the heads of the families, which once proudly called each other brother, may limit their exchanges to a courtroom. When the sale was made 65 years ago, the name of the senior member of the now-warring clan, Tang Wai-tong, was written on the title deeds, along with the patriarchs of the other two Tang clans. His descendants say the other part of the clan, comprising about 130 people, has no right to any share of the land sale - something its members bitterly dispute. Mr Tang Ying-wah, 37, is among those who may be left out of the money, and he is critical of the way in which the attempted sale has been handled. He claims his ancestor paid the $5,000 share for the land, even though the head of the other family in the clan put his name on the deeds, because he was the clan elder, and its best-known member. Mr Tang's only evidence is a battered accounts book he says has a record of the purchase. His stand has aroused resentment among the other Tangs, who want the sale to go ahead as soon as possible. A writ was filed last week in the Supreme Court to stop Mr Tang's family from claiming ownership and interfering in the sale. The District Lands Office is refusing to allow the sale to go ahead until the dispute is settled. Nestled within the disputed land is an ancestral hall, ironically called Tang Yau Yi Tong or the Tangs' Friendship Hall, built to mark the once close ties between the clans. Mr Tang is adamant his clan rivals want to cheat his family. ''We are not bothered about whether they want to sell the land or not; what we are concerned about is whether or not we are are entitled to ownership of part of the land. ''We have our account book to prove it,'' said an angry Mr Tang. Nevertheless, he said he hoped the dispute between his family and that of the other clans could soon be settled amicably. ''We used to slap each other on the back as brothers; what I really want to do is settle this thing out of court.''