4 softsleeper tickets in one compartement?

you are not guaranteed to get twice four sotfsleepers together in a compartment, as the tickets are issued randomly by the booking system and seats or berths can not be selected.
If you book as early as possible, there may be a chance for some of your tickets in one compartment.
if you are not in the same compartment, you can try to tell other passengers that you have children to take care and ask whether they are willing to change room with you.