What are the skulls representing

I just logged on and

Did you find out if you can rejoin the sameclub again if you have been kicked?

Love to see the screenshot of you on the last block

Its usually on the bottom right of the screen but im not sure if you are using a phone or tablet, that might be the difference.

You must finish the round to collect the tributes full value(5 clicks down on the volcano)if you dont finish it but uncover the card, you only get one volcano click down

I dont think its any set amount, but the more members you have working on it, the quicker the perk is filled.