Place a small heavy saucepan over medium-low heat, spread sugars over the bottom, and cook, without stirring until it begins to melt.
After that, cook, stirring constantly, until melted sugar turns a deep amber color, about 2-3 minutes.
Immediately remove the saucepan from heat and carefully stir in hot water until fully combined.
Quickly pour the mixture into 6 hot 4-ounce jars (you can place the jars in boiling water before that).
In a small saucepan over medium heat, combine coconut milk and whole milk and stir until bubbles form around the sides of the pan, but do NOT boil. Remove from heat.
In a large bowl, whisk condensed milk, eggs, egg yolk, and salt until just blended but not foamy.
Slowly stir in hot milk, stirring all the time. After that stir in vanilla, rum, and orange zest.
Strain the mixture through a fine sieve and after that pour the mixture into the prepared jars. Cover each jar with foil tightly.
Add a trivet to the 6-qt. Instant Pot and also add 1 cup of water.
Arrange the jars on the trivet, offset-stacking as needed.
Place the lid and lock it, make sure to close the pressure-release valve.
Pressure-cook on high for 6 minutes, after that, let the pressure release naturally for 10 minutes; quick-release any remaining pressure.
Cool jars for 30 minutes at room temperature and after that refrigerate until cold, about 1-3 hours.
Run a knife around the sides of jars and invert flans onto dessert plates.
Serve with fresh berries on the side.