For the lights, I think no tap_action is required, so just remove this section from the Upstairs card:
- title: Upstairs
entities:
- entity: light.kitchen
- entity: light.dining_room
...
However, if you want to customize the actions, I think you need to do it for the entities themself, and not on the group entity, e.g.:
- title: Upstairs
entities:
- entity: light.kitchen
tap_action: ...
There are some examples on GitHub.
Just as an example, this is how I configured a button for my Sonos player that plays/pauses on top. Note that I call a service, and therefore I need to pass the entity_id as service data:
...
- entity: media_player.playbar
icon: mdi:music
offStates:
- "off"
- "unavailable"
- "paused"
tap_action:
action: call-service
service: media_player.media_play_pause
service_data:
entity_id: media_player.playbar
...
[EDIT]
Apparently it is not possible to override the tap_action for a light entity (unless you are defining a custom entity card). Overriding the hold_action however works without any problems.
@DBuit is this expected behaviour? Or should it be possible to override the tap_action for a light or switch entity?