There are forty Samskaras to be performed by a Hindu.
Death is an important Samskara,
I will provide some guidelines with Links.
However, the suggestions of the Purohit is to be taken for consideration as some customs vary for each Caste and even in a Caste for a particular Family/Group.
General.
Those who become Untouchable during the period of Mourning-Theetu
The following link is very useful.
http://stotraratna.awardspace.com/sruthi/Samkshepa%20dharma%20sastram/vd4.pdf
Check list.
1.Inform Family priest, Sastrigal.
2.Keep the body lying head facing South.
3.Light an Oil lamp near the  Head;apply Vibhuti(basmam, not as a paste)
3.Light some Agarbathis to ward off smell.
4.As one is not to cook at Home till the body is taken out,inform relatives for arrangement of food for the day.
5.Inform people who are to be informed.
6.At best the body can be kept for about 10 hours;under special circumstances, it may be kept for 24 hours in an air-conditioned casket.
7.Those who go to the burning ghat must go the next day for the collection of Ashes.
8.Ensure that a Doctor visits and give you a certificate.
9.In the case of Death in a hospital, make sure that the necessary formalities are complied with and a certificate is obtained.
10.Inform the Crematorium about the expected time of the arrival of the body after consulting the Sastrigal.
11.At the Crematorium show the certificate and get a receipt. Some times it will be issued the next day.
12.Get the Death registered .
Clarifications on some aspects.
1,One can perform the ceremonies for the first twelve days at specified places,
However it is correct to perform all the Rites at Home and it will bring prosperity.
2.The rites for the first ten days may be done from the seventh day , performing the cumulative rites for six days.
3.There is still a custom in the Hindu communities. especially among Brahmins for a  Widow.
That of removing the Mangal Sutra or Thaali and breaking of Bangles in Public.
This does not have the sanction of the Sastras.
The wearing of Thaali is a later custom developed and it does not find a place in Vedic Marriage,
The removal of Mangal Sutra may be done some one who is widowed already(preferably elder to the one in question) quietly on the morning of the Eleventh Day,;have the bangles removed and have the Mangal Sutra removed and dropped in a vessel containing  milk.
One can perform all functions in the Family including Marriage after the Thirteenth Day, Subasweekara,Gruha Yajnam, except in the case of Spouse. Wife and children.
The Gruha Yajna means you are  permitted to do Yajna.
Subasweekaara means you invite Auspiciousness.
Suggestions, questions are welcome.
Additional Link.
http://indiansamourai.hautetfort.com/media/01/02/1850732936.pdf
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Dear Shri Ramanan: My cousin’s (father’s elder brother’s eldest son) wife passed away last year (27 July 2015). I work and stay in the Middle East and come to India during the time of Varalakshmi Vratham and Avani Avittam so we can perform these in India. This year the Varalakshmi Vratham is on 12 August. The annual function for the deceased will be held from 13 to 15 August. My elder brother’s vadhyar advised him to perform the Varalakshmi Vratham on 19th instead of 12th August i.e. after annual function is over. However, for me postponing will result in disruption of our schedule as my wife and I have already arranged to travel on 19th and ticket/hotel bookings are already made. Would you please give us your guidance on whether we can proceed with performing Varalakshmi Vrathan on 12th August itself? Thank you and Namaskarams.
Strictly speaking when we perform Homa on the 13th day the Theetu is off. The terms Subhasweekara indicates that we adopt auspiciousness on the 13th day. The term Gruhayagnya means one is empowered to perform Homa. Such being the case I am of the opinion that after 13th day the Theetu is gone.Subha karyas can be performed. I celebrated my son’s wedding within 45 days of my elder brother’s demise. In my opinion the Vrata can be performed as also Yajur Upakarma. Regards.
lot of changes are required in the practices being followed particularly in hindu familiies after the death of the husband with lot of uncultured and inhuman beliefs and not supported by any vedas . HUman approach is required to be spread all over the world and to be seen everybody with human touch and not inhuman beliefs.
Sir my aunt’s grandson expired. how many days theetu has to be observed by me? Thanks
Three days if it is on Father’s side. If from mother’s side it is for the day you hear the news.
Thanks very much
HI, MY FATHER IN LAW’S OWN UNCLE (mother’s brother) DIED. MY FATHER IN LAW NO MORE. & how many days theetu has to be observed. Can I do big festivals like Diwali and Pongal
Three days.You can celebrate occasions.
Dear Sir, My mother in law expired some months ago and my husband is the only son. We have performed all the rituals from the third day itself at home. We perform all the monthly rituals like masiham and shodakumbham at home. However the extra masiham thithi is during a time when I need to go out for an academic programme. Is it possible to do this function on an alternate date?
Do it in the next corresponding Thithi.