“I expect them to impeach Vice President Pence too.”
In the case where the VP was impeached first, and removed (doubtful with the current 53 GOP majority in the Senate), the President would simply nominate another VP, who would be confirmed by the same majority in the Senate. There is no law, even in the 25th amendment, which precludes an absence in the Vice-Presidency. There have been 17 such absences in the past.
Pelosi holds no place in that process. She would only become the President if the President and VP were removed at the same time, which could only happen by accident or some sort of death plot.
The Democrats are hoping the Senate will elevate Queen Hillary.
You need more enlightenment. Both houses have to approve a VP replacement that is appointed. No one nominated by Trump will get past the House.