Welcome to FT Bongo.

Had a minute, so I poke around and found that you could probably save a few bucks nesting 3 roundtrips:
SEA-AMS-DEL - NW/KL with stopover $1400
DEL-SIN Jet Air $637
DEL-BLR Kingfisher $275

But then you're risking missed connections with unrelated tickets.

I would actually look into RTW fares. You could probably even add afew more destinations and make the trip really interesting for not much more than what you've been quoted.

I'm no expert, and maybe someone else will wade in, but I think they're best booked with the airline reps on the phones.

(Also not familiar with DEL airport enough to know if you'd want to see it 4-6 times in one trip )