UnePrune
You can ski on glaciers at the beginning of May - eg Tignes or Zermatt.
However glaciers tend to be very high and they get slushy/icy easily so it's not a great introduction to skiing. Could you shift to early April? There is still excellent snow in many of the higher resorts at that time (Tignes, Val Thorens, Avoriaz, plus a couple of Austrian options) and it's cheap and uncrowded (unless it's Easter).
Pixley
For two first time adult skiiers I would recommend that you look for a resort that has a British ski school. For example, BASS or New Generation. There are others around as well. Avoid ESF (the main French ski school) - they are very hit and miss.
Honestly, I think you should put ski school quality at the top of your list, as it will make the most difference to how fast you progress and probably how much you enjoy the holiday. If you have the cash, you could consider private lessons for the two of you.
Usually, these schools are found in the resorts most popular with Brits - so that means the French mega-resorts. Three Valleys (Meribel, Courchevel, Val Thorens), Val d'Isere, Tignes, Alpe d'Huez, Les Arcs etc.
However, these tend to be pricey, sometimes ugly, and crowded. Watch out for resorts where the green learner runs are also the main way back to the resort - very scary as the good skiiers zoom down them at lunch/end of day.
A good option (and a great place to go back with the DCs) is Vaujany. This is a traditional French village with a cable car into Alpe d'Huez. So you get to stay somewhere small and pretty, but access the great skiing of the mega-resort.