Apart from Commandos Strike Force, none of the games support widescreen resolutions out of the box. For those games, enabling it requires editing of the game binaries.
The Commandos Resolution Hacker by Steven Hoefel lets the user choose the desired resolution and automatically patches the Commandos executable file. It supports all known unencrypted versions of BEL/BCOD. The program can be downloaded from this location: http://modelrail.otenko.com/electronics/commandos-behind-enemy-lines-resolution-fix
A fourth resolution of 1280x1024 is actually built into the game, but is unlisted under the game's options.
It can be enabled by opening
comm2.cfg in the
OUTPUT folder, and setting the value of MODOVIDEO to 3.
For Commandos 2, this widescreen mod can be used.