Scalpel tongue/demonstration on acting vampire.

Vampire A is acting and voting KRC what happens if it is forced to abstain?

Scalpel tongue forces to abstain, so can other vampires even participate in the vote afterwards? Since there is no For or Against votes.

Demonstration just cancels the votes of the acting minion so I imagine the situation is different. Can somebody please explain what happens here

If the acting vampire abstains - either because they're forced to or they have no votes to cast or they simply choose to abstain to avoid certain possible card plays - then that vampire casts no votes and everything else continues as normal. Every other source of votes can still be used by acting and non-acting players alike - vampires with titles, burning the edge, tapping Ventrue HQ, vampires playing cards, discarding a political action from your hand (if you didn't already play one) etc.

The acting vampire doesn't have to vote. There are still votes for and against from other sources (potentially).

Note: when the acting vampire calls a vote with a political action card, the one vote from that card goes to the player - not the vampire. 6.3.3: "If a political action card was used to call the referendum, that card provides a vote for the acting vampire's controller."