Manu Smriti ,at one place, states that re-marriages of widows are never prescribed by laws.
9.65. In the sacred texts which refer to marriage the appointment (of widows) is nowhere mentioned, nor is the re-marriage of widows
prescribed in the rules concerning marriage.
However,begetting sons through the methods of Niyoga are prescribed and allowed for a widow and her brother in law.
9.120. If a younger brother begets a son on the wife of the elder, the division must then be made equally; this the law is settled
9.190. (If the widow) of (a man) who died without leaving issue, raises up to him a son by a member of the family (Sagotra), she shall
deliver to that (son) the whole property which belonged to the
9.59. On failure of issue (by her husband) a woman who has been authorised, may obtain, (in the) proper (manner prescribed), the
desired offspring by (cohabitation with) a brother-in-law or (with
some other) Sapinda (of the husband)
But,in these kinds of cohabitation,the objective is only Dharma,i.e begetting sons.Cohabitation on the basis of lust is condemned.
9.143. The son of a wife, not appointed (to have issue by another), and he whom (an appointed female, already) the mother of a son, bears
to her brother-in-law, are both unworthy of a share, (one being) the
son of an adulterer and (the other) produced through (mere) lust.
9.147. If a woman (duly) appointed bears a son to her brother-in-law or to another (Sapinda), that (son, if he is) begotten through desire,
they declare (to be) incapable of inheriting and to be produced in
Also,regarding the marriage of a widow & her brother in law,we find the following verse,which apparently contradicts the first verse given in my answer.
9.69. If the (future) husband of a maiden dies after troth verbally plighted, her brother-in-law shall wed her according to the following
& one more,
9.146. He who takes care of his deceased brother’s estate and of his widow, shall, after raising up a son for his brother, give that
property even to that (son).
Conclusion-The events mentioned in the question all occurred during the Treta Yuga.Now, the laws of Manu, while it apply with full force in Satya Yuga, may (or may not ) apply with equal authority in Treta.In anycase,while Manu do not approve the remarriage of widows generally, allows a widow marrying her brother in law under certain circumstances.