As Salaamu alaikum wa Rahmatullahi wa barakatuhu. I want to clarify an issue about doing Umrah with a mahram. My mom is a widow and she does not have any son. She wants to perform Umrah with her sister, sister's daughter, and her sister’s son-in-law. Does the shariah allow this? Please do reply at the earliest as she wants to pay the travel agent.
بِسْمِ اللهِ الرَّحْمنِ الرَّحِيْم
In the name of Allah, the Most Gracious, the Most Merciful
No, it is not permissible for your mother to travel in this situation because her sister´s son in law is not a mahram for her.
Those people who are Mahram through blood ties are as follows;
Parents, grandparents, and further ancestors;
children, grandchildren, and further descendants;
siblings of parents, grandparents and further ancestors (cousins and their children are not Mahram);
children and further descendants of siblings
It is not permissible for a woman to travel without a mahram in Islam.
It is narrated that Ibn ‘Abbaas (may Allaah be pleased with him) said: The Prophet (peace and blessings of Allaah be upon him) said: “No woman should travel except with a mahram.”
Allamah Ibn Aabedeen Shami writes that it will be impermissible for a woman to travel the distance of three days and three nights without a mahram. However, it will be permissible for her to travel a distance, which is less than that without a mahram because of need.
Only Allah knows best
Written by Alimah Sumeyye Sofu
Checked and approved by Mufti Mohammed Tosir Miah
Darul Ifta Birmingham
 al-Hidayah p.34 v.3 Maktabatul Bushra /Quduri p.871 Maktabatul Bushra
 Bukhari 1729, Muslim 2391
 Raddul Muhtar p.465 v.3 Darul Alimil Kutub