Say yes now, as asked
You get on well with him and your parents love the match; saying yes keeps the pre-Diwali plan and your father's wish intact.
If you do this: The engagement goes ahead, but the course and the move to another city stay unresolved and may collide soon after the wedding.
Cost: Leaves the June question unasked; may put the course at risk later.
You: Tell your parents you agree to the engagement before Diwali.
The exact first sentence“I am happy with him, and I am ready to go ahead with the engagement before Diwali.”