Roof repairs - advice needed

[abg]

Evening,

New to the forum and so thanks in advance for any info provided.

Trying to deal with a leak at my fathers house. The leak has been coming from this hip end of the roof and, I think, from the dislodged/broken arris hip tiles.

All the arris tiles are fixed well but are loose but not to the point of falling off.

A few questions:
I presume that some of those hips tiles are incorrect as they are of a different shape and just look wrong? - big gaps. Maybe bodge job done at some point...?

I am tempted to remove all the tiles on the hip and replace for new. However, as one of the photos shows, there is no permeable/impermeable layer under the tiles nor battens. Each boarding slats appear to be angled to allow the tile nibs to sit on. I think this would prevent an impermeable layer being put on top as the tiles would not sit properly. As these boards are all in good condition, and the house has been water tight for over fifty years, I am tempted to just replace the tiles and be done with it. In theory, it can be watertight again. Changing the slats would mean re-doing the entire roof I think.

Final question - these sort of arris hip tiles - should they be cemented down?

Thanks.

 

[catlad]

Looks ok just need a few tiles replacing.