certain if in a sentence

It is not certain if Mr Funada will join the new party.

The doctor isn’t certain if it is necessary to operate at this point.

I’m not certain if I’ll be able to come to your party.

I have to work late tonight.

It is not entirely certain if birds descended from dinosaurs or if they arose as a totally different species.

Employees are still not certain if the closure of the company is temporary or permanent.