No, it is not true that if people write in Bernie Sanders when voting the vote goes towards Trump.
They are just trying to pressure you to vote for the candidate they want. Don't listen to them, vote your conscience, do NOT vote for the lesser of two evils.
No. But it doesn't go to Mrs. Clinton either, and if she doesn't get enough votes to win, and Sanders doesn't get enough votes to win, then Trump wins.
Splitting the Democrat vote is the probably the only chance Donnie has of beating Hillary. That is why even Bernie will support Hillary for POTUS, to stop that.
No, it doesnt count toward either candidate. Voting for any third party in the General is really stupid. Someone is pulling your leg, presumably you dont want to vote for Donald.