I do the CCU-DEL-MUC on a regular basis and the late AI/UK flight that lands around 10.30pm in DEL is usually fine for getting onto the MUC flight that leaves around 1am. Once you land in DEL you use the international transit facility where you can point out that you are running late and skip any long queues (if any). The fact that you have PRM in your party actually helps as the the assistants know they way around and use a separate PRM queue for security. If you want to make absolutely sure that you get the shortest connection book the DEL airport assistance service: https://www.newdelhiairport.in/meet-greet-services They will pick you up from the UK flight and drive the entire party with a buggy to the transit check point. They also know whom to call to hold the flight for you.

The luggage needs about 45-60 min to make it onto the MUC flight, DEL has a state of the art baggage sorrting system that does the job in 15min.

LH in DEL doesn't see that you are running late, if by chance you don't make it they will rebook you onto the later Swiss flight to ZRH oder the 3am LH flight to FRA. The luggage is automatically assigned to the new booking. Flights to/from India usually carriy additional vegetarian meals to cater to the pax who forget to prebook special meals.