The structure of peroxodisulphuric acid (H2S2O8) is

Each sulphur is having 2π bonds. Hence, total number of π-bonds in peroxydisulphuric acid is four.
The structure of pyrosulphuric acid (H2S2O7) is

Each sulphur is having 2π bonds. Hence, total number of π-bonds in pyrosulphuric acid is four.
So, sum of π bonds present = 4 + 4 = 8