I am not sure what the official policy is in regards to F and B credit per day, but since we had two adults they gave 2 vouchers for $15 per day. We stayed 4 nights, received $120 in vouchers. They allow you to use the vouchers for items in their coffee shop area, lobby bar, restaurant, etc. We used $45 to cover a few drinks and app the first day and there was no problem.
My experience has been that some properties give 2 vouchers if two adults, others just give one per room. I stay at Courtyards frequently and receive one voucher no matter if two adults or not, but I can think of a few that gave 2 vouchers for 2 adults (Courtyard New Haven Yale comes to mind in Sept).
Edit to add: If your bill comes to $26 dollars and you apply two vouchers, you lose $4 worth of the voucher. Hope I answered that somewhat clear.