So here's the question, (assuming this fare will be honored) if I made a booking but wrote 2 guest, can I bring 4-6 guests without updating the booking/paying extra fees?
+1
If it's a 3 bedroom reservation, then I'd think it's allowed!
The 2 of you will check in. Whoever comes and visits can obviously sleep in the other rooms. Making sure there are additional towels, etc.. would be helpful.
Also, if concerned, you can probably call the hotel directly in a week and ask them if there would be another charge added to your room if 4 more people came.
If they say that it's no extra charge, then you're all set!