Step 1: Identifying the Inhabitants. 
The inhabitants of Seemapuri are mostly poor migrant workers, often living in poverty and working in low-paying jobs. These workers come from different parts of India in search of better opportunities.
Step 2: What they do for Livelihood. 
For their livelihood, the people of Seemapuri primarily engage in rag-picking. They collect garbage, sift through it, and sell recyclable materials like plastic, metal, and paper to earn their daily wages.
Step 3: Conclusion. 
Despite their hard work, they continue to live in deplorable conditions, lacking proper sanitation, infrastructure, and basic needs.
  
 Final Answer:  
\[
\boxed{\text{The inhabitants of Seemapuri are poor migrant workers who earn their livelihood by rag-picking. They sift through garbage to collect recyclable materials like plastic and metal to sell.}}
\]