Hi - have a look at the Enjoy England website, for quality assessed places to stay close to the city centre:
http://search.enjoyengland.com/en-GB/Sea…
Prices start from £20 a night and all properties are in the centre. The Granville has really amazing sea views if you're looking for somewhere a bit special. Teenagers are quite hard to impress but this place should do the trick:
http://www.granvillehotel.co.uk/
Hotels with indoor swimming pools start at £115 a night for your dates:
http://search.enjoyengland.com/en-GB/Sea…
If you're looking for great ideas of what to see and do around the Brighton area, the City Breaks section has loads to offer:
http://www.enjoyengland.com/ideas/city-b…
http://www.enjoyengland.com/ideas/city-b…
Why not start with a walk around the Lanes and North Laine? The shopping is fantastic in these areas, especially for vintage clothing, arts and crafts.
Spend the afternoon down near the beach - take time to visit Brighton Pier - get yourselves a stick of Brighton rock and enjoy the quirky atmosphere. The views out to sea are amazing on a clear day and you can also see what remains of the historic West Pier.
If you have time left, don't miss the spectacular Royal Pavilion and The Sea Life Centre. Also, Cool City Walks provides audio tour guides for your Mp3 player, so your grandchildren can enjoy everything they want at their own pace - it costs just over £5 to download:
http://www.coolcitywalks.com/brighton/in…
There are lots of wonderful restaurants and bars off the main streets down from the station, where you can stop for food. Try the vegetarian and Italian places. For dinner with a difference, head to Bom-Banes. Run by two musicians, this venue offers fantastic live music nights and the restaurant staff often sing whilst serving you! Book well in advance as it's very popular.
http://www.bom-banes.co.uk/musicdates.ht…
If you're looking for something to do in the evenings, the best places are near the beaches, down on on sea front. Everything is within walking distance, so you won't need to worry about taxis or buses.
Have a great time!