It is indeed Sarvavid Vairocana, a common form of Vairocana in Tibetan Buddhism due to the popularity of that Yoga tantra practice in Tibet (Kunrig in Tibetan). For further confirmation, you can check out the Himalayan Art website: http://www.himalayanart.org/items/90176
Just a correction though, the blue Buddha is not Akshobhya but actually Medicine Buddha. You can tell this by the medicinal myrobalan fruit that is held in the blue Buddha's right hand.
You're right to think that each thangka design is usually unique. What you have is not a painted thankga, but a printed reproduction of the original. This is fairly common practice it seems, since printed reproductions are much more affordable. Painted thangkas will cost at least a couple of hundred dollars, so reproductions are often a good substitute for practitioners who cannot afford them.
The practice of Sarvavid Vairocana is rather complicated and esoteric, not particularly accessible to non-initiates. However, the famous function of that particular form of Vairocana practice is to liberate beings from the three lower realms, i.e. the practice will prevent or liberate a person reborn as a hell being, hungry ghost, or animal. From the teachings of Lama Zopa Rinpoche:
Kunrig is not a Highest Yoga Tantra deity; I think it belongs to either Yoga Tantra or Charya Tantra class. Kunrig is known as “the King of the Deities for purifying the lower realms.” Even if someone has already been born in the lower realms, if you do Kunrig practice or puja, they will be liberated from the lower realms. There is a story that when a deva died and was reborn in one of the hell realms, King Indra didn’t know what to do, so he asked Buddha for help. Buddha then manifested as this deity Kunrig and granted the practice of the Kunrig jang-wa. The deva was then liberated from the lower realms.
OM NAMO BHAGAVATE / SARVA DURGATE PARI SHODHANI RAJAYA / TATHAGATAYA / ARHATE SAMYAKSAM BUDDHAYA / TADYATHA / OM SHODHANI SHODHANI / SARVA PAPAM VISHODHANI / SHUDHE VISHUDHE / SARVA KARMA AVARANA VISHODHANI SVAHA
By merely seeing the Kunrig mantra—no need to mention actually saying it—one purifies the very heavy negative karma of avoiding the holy Dharma.
Avoiding the Dharma is more heavy than destroying all the statues, stupas, scriptures, and temples in this world; heavier than that. This means you think that Buddha’s teaching is not for you, from your heart you give it up; you give up from your heart the object of devotion.
Perhaps you feel that some things are very difficult, such as studying Buddhist philosophy; it’s difficult for you to understand. You think, “What use is this in my life?” Whenever this happens, that is giving up Dharma. These are Buddha’s teachings, so the karma is unbelievably heavy.
It has also become trendy in modern times to set mantras to music, although the pronunciation is not always the best. An example of the Kunrig mantra is here
As for Amitabha Buddha, he is (on one level) the main teacher in the western Buddhafield called Sukhavati, the Land of Great Bliss (Dewachen in Tibetan), a place that many Mahayana Buddhists aspire to be reborn in so they can complete the path to Buddhahood as quickly as possible utilising the ideal environment that was created by Amitabha Buddha's vows. His practice is therefore often associated with the end of life. The most common form of Amitabaha practice is to recite the Buddha's name (one of the methods by which people can be reborn in Sukhavati), a prevalent practice in East Asia.
Medicine Buddha is, as the name implies, associated with healing of various mental and physical illnesses and sufferings. The Medicine Buddha made 12 specific vows (like Amitabha's 48 vows), several of which relate to alleviating the suffering of sicknesses. Reciting his name and mantra are beneficial for many problems, not just illnesses. The Medicine Buddha also has a Buddhafield, in the east, called Vaiduryaprabha, the Land of Vaidurya Light.