Kindly refer to the following link:

It is not permissible to call a Muslim a kafir. The Prophet salla Allahu alaihi wa sallam said that whoever says to his brother: O Kafir, then one of them will take it (meaning one of them will be labeled as Kafir).  Therefore, one must not say this unless the conditions are fulfilled and obstacles do not exist.

Giving takfeer like this is a trademark of khawarij. One can’t give takfeer to individuals without ensuring that the conditions are fulfilled and that there are no obstacles preventing takfeer from taking place.

Video Links:

Keeping relations with people who do not pray, especially close relatives | Sheikh Assim Al Hakeem

Labeling people as kafir & how to give Dawah 2 people who don't pray or practice Islam

Do things people say against Islam when angry make them kafir?

Is it permissible to label people as Kafir? 

Giving Takfeer, Is there a process? Can layman call someone kafir who doesn't pray or calls on dead?

Those who mock Islam, are they Kafir (apostate)? | Sheikh Assim Al Hakeem (calling disbelievers, disbelievers, or kafir)

Can we call a non muslim Brother or Sister? Can we call a non muslim Kafir? 

Is my Islam nullified if I don't consider Muslims kafir if they commit acts of kufr?

Is my friend a Kafir?

And Allah Knows Best