What turn is Japan attacking the UK? How are they getting to India? By sea or by land?
If by sea, you may not be able to do much except use naval blockers. You won’t be able to stop a Japan that throws its whole weight at India. However, Australia, China, Russia, and the US may be able to do something to chip away at Japan.
-Australia- have at least one transport in Queensland to take back any islands Japan gets but cannot defend well. Use DD blockers when needed and be aggressive.
-China- Hold Yunnan at all costs.
-USA- build up a fleet at Hawaii or Queensland ready to pounce where Japan is weakest. If Tokyo can be hit Japan won’t be able to send the kitchen sink at India.
-Russia- Depends on the Europe map. If they can afford a couple mechs here and there to China they can play huge dividends later.
-UK India- take Sumatra turn 1 (take Java turn 2 if able). Retreat Malaya troops to shan state and move all available units (including AA guns) to Burma. Purchase a mix of units- I prefer a couple mech inf and some inf turn 1, turn 2 a couple art and inf; turn 3 on all inf (adjust as needed). Essentially, you want to prevent Japan from getting and holding Yunnan/Shan State. This prevents his aircraft from a landing site if he attacks India by sea. Use your surface ships as blockers to slow the Japanese fleet down. Retreat to India before the assault…
If by land, you have a bit more time, and it is much harder for Japan to commit enough ground forces to take India. Keep building up your stack and be wary of where the Japanese aircraft are and where they can hit.
In any case, you can take Sumatra turn 1 with India - and if Japan didn’t attack turn 1, you may be able to get java as well. That gives you a bit of extra money. Don’t worry about protecting Sumatra and Java- you won’t be able to. However, Japan will have to attack these and they won’t be free.