Step 1: What is asked.
We need the chief guests for India's 2026 Republic Day Parade.
Step 2: The tradition.
Every year India invites a head of state or government as chief guest to strengthen ties with that country or group.
Step 3: The 2026 guests.
The 2026 parade had European Commission President Ursula von der Leyen and Portuguese Prime Minister Antonio Costa as chief guests.
Step 4: Remove others.
The other pairs, like Macron and Biden, do not match the 2026 invitation.
Step 5: Confirm.
This choice reflected India's growing focus on ties with Europe.
Step 6: Conclusion.
So the chief guests were Ursula von der Leyen and Antonio Costa.
Answer: Ursula von der Leyen and Antonio Costa