Plot in Sense and Sensibility

In other words, Henry Dashwood has left his neice and her daughters largely out of his will in favor of his grandson, a common practice at this time that favored male descendants.  He has, however, given each of them a token inheritance of 1,000 pounds.  In dollars, 1,000 pounds sterling was worth about $5,000.  

The will prohibits John Dashwood from selling the estate's timber to profit himself.

That is, John Dashwood inherits the estate after Henry Dashwood dies, and John Dashwood's four year-old son inherits the estate after his father dies.

The "former marriage" most likely ended in the death of Dashwood's first wife.  Divorce was very rare and required a governmental decree.