yyzgigi,

I have only had experience with 2 properties on multiple rooms and it is as follows:

1 PH Toronto - 2 room for 2 nights on FFN. With one room upgrade by additional fee to a suite arranged directly with the hotel. We got 2 amenity, one for each room and Diamond breakfast in Aurora restaurant for all 4 for both mornings

2. HR Montreal - 2 rooms for 2 nights on paid corp rate. With one room upgraded to a suite by small additional fee arranged directly with the hotel.
We got 1 amenity but regency club access with breakfast and appetizer / light dinner for 5 adults and the 2 kids got breakfast coupon for the restaurants since no kids allowed in the lounge.

You would only get tier credits for 1 room. What I had done in Montreal is we check in under my name and added one designated person (my sister) as the 2nd person on the 2nd room. When we checked out, I paid for both rooms since I organized the family weekend but added my sister's new GP number replacing mine on the 2nd room with the bonus code so it gave her some nights and points to get her started on Hyatt. She was very happy with Hyatt so I might make her a convert yet. Actually her husband had a card from way back in 2002 for their trip in Vancouver but I think they either lost the points or did not get any since their stay in Hyatt vancouver was booked on a conference rate.

YMMV but hope this helps,
Mary