Can a younger sibling marry before elder sibling in Hinduism?(Especially girls)What do sastras say about this?
As per Smritis, such an act (in case of brothers) is considered as a sin.
3.171. He must be considered as a Parivetti who marries or begins the performance of the Agnihotra before his elder brother, but the latter as a Parivitti.
3.172. The elder brother who marries after the younger, the younger brother who marries before the elder, the female with whom such a marriage is contracted, he who gives her away, and the sacrificing priest, as the fifth, all fall into hell.
11.60. Allowing one’s younger brother to marry first, marrying before one’s elder brother, giving a daughter to, or sacrificing for, (either brother),..are upapatakas (minor crimes).
Verses from Manu Smriti.
But, in certain circumstances a younger brother can marry before the elder without committing any sin.
The younger brother can marry before if the elder brother is hunchback, dwarf, eunuch, or idiot, A man commits no sin by marrying before his elder brother - where the latter is either a hunch-deaf, dumb bornblind, or of indistinct speech. (75)
On one's elder brother happening to loose his virility, or to have resorted to the practice of yoga, or to a life of asceticism, or to be degraded in life on account of a sojourn to a country a residence wherein is considered degrading (i.e., supposed to degrade a man in society), one is at liberty to marry even before the marriage of such an elder brother. (76)
Likhita Smriti's chapter 1
If one's father, maternal grandfather or elder brother [does not perform] the Tapas and the Agnihotra, there is no sin in the younger brother's marrying before the elder. (104)
Usana Smriti's last chapter.
However, i have not found anything about sisters.
The Manusmriti forbids such an act for males:
- The elder brother who marries after the younger, the younger brother who marries before the elder, the female with whom such a marriage is contracted, he who gives her away, and the sacrificing priest, as the fifth, all fall into hell.
There is nothing much said for females in this regard in Manusmriti. However we see in the case of the three sisters Amba, Ambika and Ambalika, the first was the eldest, did not marry, and was reborn (i.e., did not depart to hell). So I doubt this holds for women.
Sources: Any translation of Manusmriti in the section of description of punishments in Hell. And any authentic description of Mahabharatam.
Can a younger sibling marry before elder sibling in Hinduism?
No ,negotiation of the marriage of a younger brother before that of his elder is considered as a sin according to Garuda purana – Achar kanda –Chapter 105 - Page 245
गोवधो व्रात्यत्यास्तेयम्रुणानां च परिक्रिया |
अनहिताग्निताsपण्यविक्रय: परिवेदनं ||12||
भृताचाध्ययनादानं भृतकाध्यापनन्तथा ||
पारदार्य्यं परिवित्त्यं वार्दुष्यम् लवणक्रिया ||13||
The following sinful acts , viz. , cow killing ,robbing of Brahmana , non repayment of one’s debts and non discharge of one’s monetary obligations , non keeping a sacred fire by brahmana , or his engaging in any sort of trade or merchandise , marriage of a younger brother in the unmarried state of his elder , tutelage under one’s own servant , or acceptance of any gift from him , going on to another man’s wife ,negotiation of the marriage of a younger brother before that of his elder , creating a breach among friends and relations for money , tuition for pecuniary considerations , sale of salt.
So marriage of younger sibling (male) before elder is not allowed.
Chapter 20 of Vasishtha Dharmasutra prescribes atonement if younger sister/brother married before elder sister/brother:
He whose younger brother married first shall perform a Krikkhra penance during twelve days, marry and take to himself even that (woman whom his brother wedded). (7)
Now he who has taken a wife before his elder brother shall perform a Krikkhra penance and an Atikrikkhra penance, give (his wife) to that (elder brother), marry again, and take (back) the same (woman whom he wedded first).(8)
The husband of a younger sister married before her elder sister shall perform a Krikkhra penance during twelve days, marry and take to him that (elder sister).(9)
The husband of an elder sister married after the younger one shall perform a Krikkhra penance and an Atikrikkhra penance, give (his wife) to that (husband of the younger sister and marry again).(10)
The seventh verse prescribes atonement for elder brother if younger brother married first.
The eighth verse prescribes atonement for younger brother if he married before elder brother.
The ninth verse prescribes atonement for husband of a younger sister who married her before the marriage of his wife's elder sister.
The tenth verse prescribes atonement for husband of a elder sister who married her after the marriage of his wife's younger sister.
Prayaschitthas(Atonement) are usually prescribed for sinful activities. So, according to Vasishtha Dharmasutra, marriage of younger sibling before elder sibling is not recommended.