Presumably, you're referring to the "Trevor Thom" manuals, not the "Jeremy Pratt" ones?
For a PPL, TT vol5 is not necessary, JP vol5 is Human Performance & Flight Safety, so is necessary. TT has 6 volumes required for the PPL (1-7, not including 5), JP has 5. Choose the set recommended by your school, or you may risk some confusion because your instructors won't be familiar with them.