White King with only one Bishop can not force checkmate! The game will be a draw. But it is quite a different matter with double Bishop.
Take care of the 50 move rule or else you may have to concede a draw inspite of such a huge material advantage.
The Bishops are succeptible to attack from the sides by the opponent's King.
1.Kd2
Kd7
Coming towards the center
2.Kc3
Kd6
3.Kd4
opposing!
3...Ke6
4.Be3
Kd6
5.Bc4
Ke7
6.Ke5
Closing in...
6...Kd7
7.Bb5+
Kc7
8.Bc5
The double Bishops instantly create a wall of defense and block the King.
8...Kc8
9.Kd6
Kd8
10.Bb6+
Kc8
11.Ba6+
Kb8
12.Kc6
Ka8
13.Bc5
Kb8
14.Kb6
Ka8
15.Bb7+
Kb8
16.Bd6#
Checkmate! 1-0