I have children age 12 and 14 can we stay in one room cause all girls
You can booking a tripel room or double room with get extra bed
You can get a room with two beds and they can sleep in one and you can sleep in the other, but I would urge you to reconsider staying at the Shinjuku prince with such young girls. Kabukicho can be rough and kind of seedy at night and it's right outside the hotel and one block over. It's not really appropriate for young kids.
Capital Tokyu Hotel has bigger, nicer rooms for a similar price in a less seedy area. It isn't as centrally located, but would be more appropriate if you're traveling with 12 and 14 year old girls.
Get an answer from Shinjuku Prince Hotel staff and past guests.