Ski in/ski out often isn't great for complete beginners as it's naturally on a slope.
We stayed here over Christmas week last year.
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Rauris is a dinky resort, but it is good for beginners and intermediates. The link is an aparthotel, so self-contained apartments (our 2 bed one was huge), but all the facilities of the hotel, so restaurant, swimming pool, child-free spa. It's in a lovely little town. There's not loads else to do, but at that age, I imagine the children's days will be filled with sledging on nursery slope, lunch, nap, swimming. The nursery slope is directly next door and free to access by anyone.
The mountain is very accessible to non-skiers, I skied past many a dog walker. So if the grandparents felt up to it, they could get the gondola up to the 'middle station' (first stop) and either meet you at the pub there for lunch, or walk along a lovely,fairly flat blue, to the next pub. They could then get the chair lift down from there and have a flat walk back to the hotel. Or if they were feeling adventurous, they could take the toboggan run down.
You won't need any transport at all once in resort. We got the train from Salzburg and then the local bus from the train station, but a taxi back to the station on our return. It's just over an hour on the train, or about a 90-minute drive. Once you're there, the slope and gondola are literally on the doorstep. The pool and spa look out over the nursery slope.
It's not huge, but it's very pretty, and the charm of the traditional Austrian town might well suit your non-skier requirements. However, if you enjoyed Tignes, then it might be too small for you.
Alternatively, Les Arcs. Though I can't comment on accommodation other than in 1800. The skiing is absolutely perfect for you, and an email today told me that Arc 1950 is celebrating its 20th anniversary this coming season, so there's loads of things planned there. However, your non-skiers may feel a bit trapped if you stay there. 1800 has more going on and a big public pool, but it's still very much a French mega resort, so I'm not sure how well it's set up for non-skiers. Staying in 1600 would give easy access for the funicular back down to Bourg.