My grandfather left no will and he left behind a land with the title still under his name.He has 6 surviving children, one deceased.Who automatically inherits it? Will the lot be equally divided among the surviving children only? How about the children of the deceased ? Do they have a claim on the land too?

Legitimate children and/or descendants ARE THE PRIMARY compulsory heirs. Under the Rules of Court, an estate may be devolved through EXTRAJUDICIAL settlement, by mutual agreement among the heirs. This method requires that the deceased left no will and no debts, and that all the heirs are of legal age (although minors can be represented by judicial or legal representatives). The heirs simply divide the estate among themselves as they see fit, by means of a public instrument, and this document is thereafter filed with the Philippine Register of Deeds. A sole heir may adjudicate to him/herself an entire estate by means of an affidavit filed in the Philippine Register of Deeds.

I guess you are the child of the deceased heir. Make sure your parent is included in the extrajudicial settlement. At least 1/6 of the total worth of the estate. Get a lawyer to make sure.