How did Jay Gould and Jim Fisk decide to try to stop Vanderbilt?

because people want them to

Jay Gould and Jim Fisk decided to try to stop Vanderbilt issuing false stock of the Eerie Railroad. Vanderbilt spent millions of dollars buying this false stock, so he had to recognize Gould and Fisk control of the Eerie Railroad. The Tammany Hall was also involved with them, which resulted in a later legalization of the falsely issued shares.