Editing in an Academic Journal
They need to give a citation, but, if it is permitted to quote the entire paragraph, then they don't need permission from the other authors.
Whether it is permitted or not is a question of copyright and fair-use exemptions. If they still hold copyright jointly, then each of them needs to give permission. If your journal holds it then I see little problem as the journal can grant a license. Otherwise permission should be sought from the copyright holder for a long quotation.
Even if the old paragraph is paraphrased rather than quoted, a citation is required. Otherwise it is self-plagiarism. In that case, the copyright issue would disappear as there is no &quot;copying&quot;.
But I don't see any reason that the other authors on the old paper need to become co-authors on this one. Certainly an individual can extend old joint work as a single author.