Yevamot 44 - Four brothers
If there were four brothers who were married to four women, not related between themselves, and then all four brothers died, the oldest of the remaining brothers can - if he wishes - take all four as his wives in yibum.
This ruling, however, raises many questions. Since the Torah, in describing yibum, said, " And the Sages of his city will summon him and speak to him ," we understand that they give him an appropriate advice. If he was old and she - young, they would tell him, "What do you have in common with such a young woman? Find somebody more appropriate for your age and don't bring strife in your house." They would say the same if the ages were reversed.
Since most people will have difficulty supporting four wives, how do they let him do it in this case? - We must answer that we are dealing with a situation where he has the means. But if so, what is the novelty? It is obvious! - The ruling gives him a good advice: he should not take more than four wives, so that he can fulfill marital obligation with each one at least once a month.
If one re-marries his ex-wife, who married someone else in the interim, the child is a mamzer. That is only the opinion of Rabbi Akiva, but the Sages say that a mamzer is born only through a liaison with a married woman or a similar serious transgression. All agree, however, that if one divorced a woman and the married any of her forbidden relatives - then the child is indeed a mamzer, because in regard to in-law relationships, a divorcée is like a wife.
Art: Portrait Of A Young Woman In An Interior by Gustave Caillebotte