Assuming you have Australian passports valid for at least six months, you can obtain visas on entry for all the ports you are visiting with the exception of those in India. According to the Sydney office of India Tourism, since you are visiting several ports in India you will need a multiple-entry visa, obtainable from VFS Global vfsglobal.com. Note that an e-visa, which is valid for entry at several of India's international gateway cities, is not valid for entry at Mumbai. Also, the Indian e-visa allows for just one additional re-entry, provided it's within 60 days of the initial entry.