Question Summary:
Should I boycott my cousin or be friendly to him?

Question Detail:

 
I have a cousin who had illegtimate relationship, had kid and married the same lady. As a Muslim, I do despise his actions, but I still need to understand how I should socialize this person? Boycott him like the rest of the relatives, keep a distance but be friendly? need advice.
Secondly, is it appropriate to invest in projects that are initiated by people who may not have all that authentic background - have black money?

Answer :

In the Name of Allah, the Most Gracious, the Most Merciful.
As-salāmu ‘alaykum wa-rahmatullāhi wa-barakātuh.
Sister  in Islam
Islam teaches us to dislike evil and immoral actions, and to distance ourselves from immorality. Islam also encourages us to join family ties under all circumstances.
In the enquired case, your cousin made a mistake and later on tried to correct himself by getting married, which is a sign of remorse and repentance on his side. The Prophet (Sallalaahu Alayhi Wa Sallam) is reported to have said:
  قَالَ رَسُولُ اللَّهِ صَلَّى اللهُ عَلَيْهِ وَسَلَّمَ: «كُلُّ بَنِي آدَمَ خَطَّاءٌ وَخَيْرُ الْخَطَّائِينَ التَّوَّابُونَ» هَذَا حَدِيثٌ صَحِيحُ الْإِسْنَادِ
‘‘All the children of Adam commit mistakes and the best amongst sinners are those who repent’’[1]
We advise you to show support, friendliness and have a close relationship with your cousin with the intention of joining family ties, which is a praiseworthy action in the sight of Allah Ta’ala. Encourage your relatives to do the same Inshallah. Boycotting him is not the correct approach,  it may cause division in the family at present and many generations to come.
 
In order for us to advise you, elaborate on the project you refer to.
Who are the people you refer to not having authentic background?
 What do you mean by background?
 What do you mean by black money?
Jazaakallah
And Allah Ta’āla Knows Best
Saeed Ncane
Student Darul Iftaa
South Africa 
Checked and Approved by,
Mufti Ebrahim Desai.