Have only not gotten welcome drink vouchers twice with keys at check-in (once at the Sofitel Montreal and once at the Fairmont Royal York in Toronto). Have always redeemed them for cocktails (e.g. Old Fashioned); was later told only once (at Sofitel Montreal) that policy is for wine or beer only, but they let it slide anyway. Otherwise they seem to be consistent in providing the vouchers and letting them being used for any drink without issues.

Have only had multiple rooms booked twice; once (ibis Munich Arnulfpark) they provided vouchers for all people in all rooms; the other time (Fairmont Queen Elizabeth in Montreal) it was just for my room.

Have always gotten vouchers for the number of people booked in my room, including kids. Fairmont Chateau Laurier in Ottawa was especially generous and made a point to say the kids vouchers could be for "grown up" drinks too if my wife and I needed it (we did!). Great team there.

When travelling with the family, having us all go to the bar for the welcome drink is usually not feasible. Have almost always been able to get the welcome drinks "to go", though the bar at Fairmont Queen Elizabeth in Montreal needed convincing, and was reluctant to let me borrow a tray to bring it up to my room, and wanted it back "as soon as you're done". Overcrowding at the hotel bar prevented getting a welcome drink at Fairmont Chateau Frontenac - my wife asked to take them up to go, which would have helped with the overcrowding rather than bringing down a family of 4 at peak hour, but they refused. Maybe it's a Quebec thing about bringing drinks to rooms?