Dual caps are simply two caps in the same housing, normally sharing a terminal. In the case of 37 and 38 the two caps with the common terminal is clearly seen in the schematic. But that common is not ground! You should check that! In the case of 19 and 20 the common terminal is grounded.
In the early days they used common cans with multiple caps inside to save space and cost but nowadays single caps are tiny in comparison so there’s no need to do that. So all these dual caps can be replaced with single ones.