Is Sutak to be followed by all members of family including relatives?

They should postpone it till the Naam Karan of the kid is done. But these days people don't follow it and do things which were actually fixed before the birth of a kid in a family.

Sutak is generally observed in Hindu families after the birth of the child. Though the most common time period for observing this is for 10 days and in some communities it even extends for 21 days but in earlier times depending upon the situations and requirement this time was selected from 3 to 11 days.

The main reason behind observing sutak was that as mother was under recovery period she was not allowed to go to kitchen and religious places for any work. The new born baby is also prone to infection and it is better if the mother and baby are not allowed to mix with others. So there is some scientific reasoning behind this and people following blindly this ritual do not understand these things.

In todays modern life depending on the circumstances one can take a decision to cut down this sutak period but definitely the baby and mother should not be disturbed for at least a week or 10 days till they are fully recovered and resistant to the infectious attacks from outside.

In earlier times certain things were prescribed to be followed due to some practical reasons but later they became a matter of belief and blind faith and we should use them logically and rationally rather than having unnecessary religious fears in our minds.

Sutak will be observed for 10 days minimum and maximum 21 days after the birth of a child in the family. All the families who are having the same family name are supposed to observe this sutak. The newly born baby and the mother will be treated carefully. If all the members start going and touching them there will be many chances for the child to get infections and that may lead to unwanted complications. To avoid these complications and to keep them safe this custom has been introduced. In some families, the father of the child is not allowed to see or touch the baby. On the 11th day the first time, the face of the baby will be shown to the father in the oil and then only he will be allowed to see the baby. The very idea of following this custom is to see that hygiene is maintained and proper care is being taken for the health of the baby.
All the people who are having the same family name should observe this sutak. They are not supposed to go to the temples or they are not supposed to enter the pooja room in the house also. On the 11th day, they will have to have a head bath and then they can perform all the rituals as usual.
This is not a superstition and there is scientific reasoning also in this.
Coming to the question of performing the marriage, if the family name is the same we are not supposed to perform the marriage in that Sutak period. Generally, they will see such issues also before deciding the auspicious date for the marriage. If the family name is different then there will not be any problem. But the family which is having sutak are not supposed to attend that marriage function.

Sutak is a celebration observed after the birth of a newly born child in a family. The date of celebration could be somewhere between 11 days and 21 days considering the convenience of the family. Under that situation, known relatives and other aquanated people are invited to witness the function when a Naam - Karan sanskar also follows. In the earlier days, it ranged from 3 to 7 days.
The philosophy behind following Sutak is to allow both mother and newly born child to have ample rest for their speedy recovery. In the family, other members too maintained distance in touching the child so that no infection develops. Even the mother did not enter kitchen for the same reason.
Though however, the medical science insists to follow proper hygiene for both mother and the baby and the mother should follow healthy diet as recommended by the doctors and the baby should be provided the mother's milk maintaining cleanliness.
With the change of time, we are not so rigid regarding the fixed date of Sutak but we attach importance to the healths of both mother and the baby.
To postpone marriage with the probability of Sutak in your cousin's family would not be a wise decision since any deferment may compound the problem within the two families negotiating marriages.

!. If the marriage date is not fixed:
In this case, if the relationship is such that they fall in the relativity to follow Sutak as per the family's or community's tradition and practice , then the marriage date ma be fixed factoring in the Delivery due date and Sutak period with sufficient margin.

2. If the marriage date is fixed and arrangements started:
The postponement will cause financial loss, cause inconvenience and disturbance to all who were invited ; and the sentimental and emotional stress to both the boy's and girl's side. Hence practical suggestion is to conduct the marriage as planned.

Whatever be the decision, it should be taken by the mutual discussion and consent of at least the immediate people of the bride's side and groom's side. Once decided there should not be any iota of doubt in mind and should not mind any other comments coming.

All the best.