Wrap them in begin/end cutscene action parts or hide/show cursor action parts. Don't forget to untick
the "always allow to skip active text
" option under the game properties
tab under the game
section (cog icon on left hand menu).
Cutscenes can be skipped with the escape (esc) key though, so if you want to completely disable skipping then use the hide/show cursor action parts found under miscellaneous