You can't promote to a King (or a 1pt Q) in a regular game. only if promotion is set to =King, or it's Antichess.
If a player has multiple kings, only one of them is the real, vulnerable king. The other kings will behave like ordinary pieces. Think of them as knights that move like kings.
You can set a starting position with muliple kings but only one king will be the real king. You can't really tell other than by the legal move indicators which one is the real king
, unless it's N-Check, where kings wear a number. It's usually not hard to figure out / keep track of.
In edit position, you will notice that the FEN4 is extended if multiple same color kings are detected:

you can set which ones are the real kings by editing the squares ("h1,a8,g14,n7-") in the Fen4 and clicking "Load".
The standard behavior is that you can choose what you want (Q, R, B, N) and the pieces will have normal points value.
Alternatively you can set which piece all pawns will promote to, without players being able to choose.
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Premoving a promotion will choose a queen for you (if there is a choice). Antichess: King
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You can also set which rank pawns will promote on. If not set, it will be 8th for FFA and 11th for Teams games.