A number of tiles on the edge of the roof seem to sitting higher that the other tiles or lifting

Hi Anthony, If the tiles are on the gable end of the roof and sitting on a brick wall sometimes the timber rafters can relax over creating a small gap where they join the next row of roof tiles. This can compromise the roofs integrity allowing water ingress. I would advise you to get a roofing contractor to carry out a free survey it can be fixed by lifting tiles and packing up the tile battens to counter the drop. this operation can take a few days and would require scaffold access.