I would stay away from any kind of external frame pack for this application. There are a wide variety of suitable internal framepacks available - the main problem is to get one that fits you properly and that will be comfortable when you carry it for long periods. My preferences formerly ran to more expensive mountaineering brands because that used to be the only way you could obtain quality construction. I have a feeling that many inexpensive brands now hold together quite well.

You would probably be happy with a pack with about 4000 cu in capacity (roughly 65 liters). Size down from that for other family members. Plan on them being aboe to carry about 25% of their body weight.

See the archives for previous discussions of this subject. I would recommend Kelty for a reasonably priced, well designed and well built pack.