there are 48 european and more or less same numbers of Asian Airlines operates to Delhi.If you land at the Indira Gandhi International Airport there is free shuttle bus to domestic terminal (Old SufdarGanj Airport )which is otherside of runway  shuttle bus runs every 15 minutes and free which goes thru inside crossing the runway.If you arrived at delhi and have more than three hours transit  stay at international transit lounge.Security try to push you early but dont listen them just tell them i have enough time and want to stay here otherwise i will speak to your manager?International transit lounge is clean,has AC,Toilets are reasonable and has nice sofas to lie down.There are three Air lines which operates Delhi to bagdogra,Jet Air,Indian Airlines and cheapest one is budget airlines Deccan Air.Ticket costs Ic3000/=to 4000/= depnding seasons and demand.I normaly(2 tmes) prefer Jet Air because I can buy Jet Air Ticket in London using my credit card which is around £80/= one way.Jet Air and Indian Air gives 30KG baggage allowance where as Deccan gives 15Kg only. there are some flights goes to bagdogra via Guhawati some are direct.On my return journey I fly from KTM to delhi because I dont have to recheck in at delhi.If you show your confirm connecting flights at KTM they will take you to transit hall from the air craft after a while respective airlines rep will come to you and ask you to recognised your luggege and give you the boardin pass for the onward journey.

hope these information is enough for you if you need any more dont hesitate.Once I have travelled to Biratnagar by train( RajhDhani express to Katihar) also.now you can get reservation of Indian Railway In Nepal also.There will be broad guage line before March to Jogbani and there will be direct trains to Delhi,Calcutta and Patna from jogbani.iN Nepal Dugar Brothers is Indian Railways authorised agent.Your relative can buy ticket and they can send you tickets by email you just have to print out ticket.At Delhi air port you can get pre paid taxi or DTC shuttle bus or Bus service run by Bhut Purva Sainik towards down Town and railway stations.They allow you to take luggege and costs you Rs50/= may be now gone up I'm talking about May 07.