I started with the first iPad, I bought a 32GB WiFi version. I was doing just fine with it. I had a lot of stuff on it and it was great. A year or 2 later I won an iPad 3 WiFi from work, but it was just 16GB. Based on my usage of the original iPad I thought I could get by with 16GB. I deleted a lot of the non essential items and since I didn't use the music that much stripped out the music files. I had some apps that kind of duplicated one another since I couldn't decide which I liked better and I also deleted a lot of photos since I also realized that I didn't need to cary around that many photos. I also stored most of my Kindle and iBooks in the cloud. 16GB worked just fine for me, but I also to watch what I was doing because storage space was tight. I couldn't just keep a movie on it, I watched it and deleted it. Netflix or renting movies works better for this. Take what you need and leave the rest behind
For what the original poster said his wife and daughter would be using the iPad for, 16GB should be enough, but they may find as they use the iPad more and more they may start to need more space. It all depends on how they use it. Everyone can sit here and say 16GB is not enough space, but for a large number of people it is.
This past summer though, I took advantage of AT&T's next program and graduated to an iPad4 with 64GB of storage and WiFi + Cellular. It is working great for me. Part of the reason for getting the newer iPad was because of the storage limitation of the iPad 3 that I had. I was growing out of the 16GB, plus I had bought an iPad mini with 64GB and was used to having the larger amount of storage. I wanted both iPads (the mini and the regular size) to pretty much have the same things as far as apps go.
For what the original poster said his wife and daughter would be using the iPad for, 16GB should be enough, but they may find as they use the iPad more and more they may start to need more space. It all depends on how they use it. Everyone can sit here and say 16GB is not enough space, but for a large number of people it is.
This past summer though, I took advantage of AT&T's next program and graduated to an iPad4 with 64GB of storage and WiFi + Cellular. It is working great for me. Part of the reason for getting the newer iPad was because of the storage limitation of the iPad 3 that I had. I was growing out of the 16GB, plus I had bought an iPad mini with 64GB and was used to having the larger amount of storage. I wanted both iPads (the mini and the regular size) to pretty much have the same things as far as apps go.