traveling with 4 children

hi
how schooled we book the train, if we want to travel soft sleeper with 2 parents and 4 children? is it possible to book just 4 seats and sleep there with all the children? the children are 8, 8, 10, 12 year old. place would be enough. or are we obliged to by 6 tickets? could we take another 2 tickets normal seats? and the children sleep just in the night with us in the soft sleepers?

greetings