Short answers, pulled from the story.
The name Raj Ghat translates to Royal Steps, referencing the physical climb from the banks of the Yamuna River up to the memorial site. Old Delhi sits on the west bank of the river east of Daryaganj near the historic location known as Shahjahanabad.
Mahatma Gandhi died on the 30th of January 1948 and his remains were cremated two days later on the 31st of January 1948. A black marble platform rose to mark that exact location of his death and cremation with an eternal flame burning at one end today.
Lal Bahadur Shastri served as the second Prime Minister until his death on the 11th of January 1966 and his final resting place is marked by Vijay Ghat. Indira Gandhi the third Prime Minister died on the 31st of October 1984 and her memorial is called Shakti Sthal while Rajiv Gandhi the sixth Prime Minister rests at Vir Bhumi.
Alick Percy-Lancaster served as Superintendent of Horticultural operations with the Government of India and performed the original landscaping work across the entire memorial complex. The design choices included hard materials like black marble for the main platform which created a stark visual difference from traditional Gandhian low-cost housing architecture principles.
The government of India under Atal Bihari Vajpayee made a decision in 2000 to not create separate memorials for different leaders anymore because existing memorials already occupied over 245 acres of prime land in Delhi. This land constraint forced a policy shift regarding future additions such as the delay in erecting a memorial for P. V. Narasimha Rao who died on the 24th of December 2004.