Hi sista, welcome to BB.

Why do your children fight? If it's over a toy then I'd say if they can't play nice with the toy they don't get the toy at all - that's it for today and tomorrow. If you can encourage them to talk out a problem rather than fight I'd try to do that. As for hitting a sofa, that's a great way to release tension without hitting a sister so I wouldn't be trying to stop that just yet.

Discipline means to teach, not to punish. You can discipline your children by rewarding good play and playing with them too.