Commonly, "cousin" refers to a "first cousin", people whose most recent common ancestor is a grandparent. A first cousin used to be known as a cousin-german, though this term is rarely used today. More generally, cousin is a type of familial relationship in which people with a known common ancestor are both two or more generations away from their most recent common ancestor. This distinguishes a cousin from an ancestor, descendant, sibling, aunt, uncle, niece, or nephew. Systems of "degrees" and "removals" are used in the English-speaking world to describe the exact relationship between two cousins (in the broad sense) and the ancestor they have in common.
The Prophet Muhammad (SAWA) himself declared the names of his Ahlul Bayt who are Aal-e-Mohammad (AS) as Ali, Fatima , Hasan and Husain (AS).
The names of Ahlul Bayt are in many authentic Hadeeths narrated in Shia and Sunni books e.g. Saheeh Muslim , Hadeeth number 4450 narrated from A'ysha that the Prophet covered himself , Ali, Fatima , Hasan and Husain and declared that they are his Ahlul Bayt. It is also mentioned in Musnad Ahmad Ibn Hanbal , Hadeeth number 2903 and in Tirmithi , Hadeeth number 3129, and Sunan al-Kubra by al-Nasaa'ee, Haddeth number 7169, and Sunan al-Kubra by al-Bayhaqi , Hadeeth number 2665 and many other main Sunni books.
There are advantages and disadvantages to marrying closely (like a first cousin). Sometimes the advantages, such as having greater trust, might outweigh the disadvantages. To my understanding, occasional close marriages are not usually a problem with genetics, rather, problems tend to arise when people do this over a long span of generations. Also they have been common in many cultures not just among some Muslim cultures. Genetic problems can also arise in any marriage. However there is nothing in Islam recommending this particular type of marriage.
Yes. No non Mahram man should be allowed to see your photo with out Hijab.
You should do whatever you can to prevent non Mahram men to see your photos with out Hijab.
Yes it is allowed. She is like his cousin, so marriage is permissible between them.
Cousin brothers are Non Mahram for their cousin sisters, no matter whether they grow up together or not. Allah (SWT) who created us knows the best and He allowed marriage between cousin brother and his cousin sister, as the marriage between Imam Ali (AS) and Lady Fatimah (SA). This means that cousins are non Mahram because marriage between them is permissible.
Imam Ali (AS) has married Lady Fatima (AS) who is the daughter of his cousin Muhammad (SAWA).
Yes he can