Please guide me Nitrocontin and Deltiazem and Metoprolol together

hello
please guide me
my friend is 65 years old , and he use Nitrocontin 2.6 with Deltiazem 120 and Atorvastatin
but doctor told for better control blood pressure and heart , add Metoprolol
now i have question is there any side effect if he add Metoprolol ?

is there any problem or side effect if person use Nitrocontin and Deltiazem and Metoprolol together ?

and another thing is the other doctor told don't using Nitrocontin and start Metoprolol but my friend use several years Nitrocontin and i think there is side effect if he don't use Nitrocontin from now , so is this correct ?

i hope you guide me
and sorry for my english and if it's possible please guide e easy
thank you