My family prefer Grand Hyatt for the ground and better club, however, if you plan to use free night cert in March, you might have to settle at hotel with standard room availability.
Are you 1+3 or 2+3? Based on children's age and if you are 2+3, you might need 2 rooms.
My understanding is you can't combine 2 awards. If you are successful in getting free nights using free night certs, I don't believe you can add club access award on top of it. For you to use your club access award, it will have to be a paid nights or using points.