If they are in the rightful order as the painting say it means that the represent:
- Buggy is death
- Shanks is famine
- Teach is war
- Luffy is conquest
But if we will look on the rightful order as it is in the New Testament whole order is switched. The order of them might be as well order of when they got their titles from the first one to the last one. In that scenerio
- Shanks is conquest
- Teach is still war
- Luffy is famine
- Buggy is death
But wait there is more: sword is wield by the war
if teach looks different there might be still some differences as he might represent death as well