I was just in Twickenham this week although didn’t stay at a hotel. There is a large Travelodge Hotel right next to the train/bus station but it’s only a 12 minute walk up the road to the stadium. The more interesting restaurants in Twickenham are a 5-10 minute walk down the road to the center of town and the Thames. There are a couple of nice river pubs in Twickenham, one near the Teddington Locks and several in Richmond, a 45 min stroll or a quick bus ride from Twickenham.
EDIT: The other two hotels that were recommended to you both look very nice and you’d probably be comfortable at either. If you are looking for an interesting area as well as a hotel, I’d pick the one in Richmond, my favorite area. If you are going to be at the conference and just need a place to sleep it won’t matter.