I assume as follows

Left hand side (LHS)– incomer 800 Amps

Right hand side (RHS) Incomer 2500 Amps

Bus tie 2500 Amps

Then both buses to be rated for 2500 Amps.

If Bus tie is 800 Amps then LHS bus to be rated for 800 Amps and RHS bus to be rated for 2500 Amps

All the buses to be rated for 50kA for one sec.

How did you arrive at the 50 kA,have done the short circuit calculation.