Is it OK to write first initial of some authors on a paper and full first name of others? Suppose there are two authors Albert Einstein and Isaac Newton on a research paper. Is it OK to write them as A. Einstein and Isaac Newton or vice versa? Similarly, if there are more authors, is it OK to write initials of some of them and not all? If it is not OK, is it wrong and unacceptable, or bad? 

My question is about writing the authors' names on the top, with the title of the paper.
Usually, this is determined by the style guidelines of the journal or conference, so all author names should be formatted in the same way. There are cases, however, where one author consistently uses an initial as his first name, or even, where an author has an initial as his first name, leading
to a non-uniform formatting of authors' names (e.g.,
Deepak Kapur, G. Sivakumar, Hantao Zhang: A path ordering for proving termination of AC rewrite systems or Zhou Chaochen, C.A.R. Hoare, Anders P. Ravn: A calculus of durations).