Having done a long journey 2 up (on a 950 KTM) I think the best advice would be for your partner to pass their bike test, if they havent already, and go on two small bikes rather than one big one. Make sure the bikes are the same and then spread the spares and luggage across both bikes.

Also, check the price of your carnet. They are issued based on the value of the bike so new (expensive-ish) bike will equate to an expensive carnet, entering India makes your carnet expensive as well.

Finally go on small fuel efficient bikes, you will get the benefit of big bikes in Europe, Australia etc but they will be completely wasted elsewhere. Looking back I would have picked an older xt600 for the trips, pay about 1000 quid or so for each bike and go from there.