For the first of your questions, see the replies to this similar discussion: https://www.researchgate.net/post/Can_a_conference_paper_be_published_in_a_journal
Concerning your second question: If a journal publishes many weak conference papers, this would have an influence on the impact factor. But good journals reject such papers.
Yes, conference papers can be submitted to journals. If you want to know a few handy tips on publishing in a Scopus-indexed journal, check out this insightful blog: https://allconferencealert.net/blog/tips-to-publish-scopus-indexed-journals/