"I have to split my rooms into 2"
If I understand you correctly..... The answer would be to list your beds on both sites and update the availability of the beds on both sites when you recieve a booking for them.
For instance, when you get a booking on hostelworld, You would then log in to your hostelbookers backoffice and remove the ability for them to sell a bed that hostelworld has sold for you, so as not to get a double booking.
After doing it a bit it will be very easy.