I think you may try to make your desired cells read-only and editable accordingly, see the demo:
Also, you may try to protect a worksheet and then specify which cells you want should be editable, all other cells would be locked, see the sample code:
e.g
WebWorksheets sheets = GridWeb1.WebWorksheets;
WebWorksheet sheet = sheets[0];
//Since all the cell are locked by default same as MS Excel.