The main essentials of cacti are: MAXIMUM SUNSHINE (window essential), watering about once a fortnight (ONLY if completely dry) in the summer ONLY. Keep away from frost but not over warm.
If you can't repot them after 2-3 years, feed with maxicrop or phostrogen.
If they are the kind to flower when reasonably young they should flower given a lot of sunshine! If not, they may have to grow quite large, like this one (which is nicknamed 'Mother in law's cushion' )- which was growing in a very large bucket.