Advice on when to harvest

Shallots - some of my shallots are really starting to wilt over, which I know is a sign that they should be harvested. However, they don't have much of a skin yet (just a single very thin layer in places). Should I leave them in the ground, or lift them and leave them in the sun?

Potatoes - 2nd earlies have been in 13 weeks but some of them are starting to wilt over and the foilage is looking very limp and pale. Seems a bit early for this to happen?

Shallots - some of my shallots are really starting to wilt over, which I know is a sign that they should be harvested. However, they don't have much of a skin yet (just a single very thin layer in places). Should I leave them in the ground, or lift them and leave them in the sun?

The natural division and bulb growth of shallots tends to force the foliage nearer to the ground, but they will still be contributing to the bulb development. The foliage will then start to die off, at which point you can ease them from the ground for a few days to start the maturing and drying process. The bulbs will then need to lifted, separated and properly dried to make sure they store well.

Potatoes - 2nd earlies have been in 13 weeks but some of them are starting to wilt over and the foilage is looking very limp and pale. Seems a bit early for this to happen?

Once the foliage has died back that's about it for spuds, and there is always the possibility they have suffered some sort of problem causing that to happen too early, and this year drought is another potential cause. Dig up the most "gone over" plant and see what you've got; if the yield is poor leave the others for as long as possible.