There seems to be some confusion here. I’ll try to unpack this.
Using Hand of Healing as an action.
Hand of Healing says:
As an action, you can spend 1 ki point to touch a creature and restore a number of hit points equal to a roll of your Martial Arts die + your Wisdom modifier.
If you use Hand of Healing as an action, you cannot use flurry of blows because flurry of blows says:
Immediately after you take the Attack action on your turn, you can spend 1 ki point to make two unarmed strikes as a bonus action.
Hand of Healing is not the attack action. Using Hand of Healing in this way allows for a single use of the healing.
Using Flurry of Blows
As mentioned previously, using flurry of blows as a bonus action requires that we first use our action to take the Attack action. When we do so, and use flurry of blows, Flurry of Healing and Harm says:
When you use Flurry of Blows, you can now replace each of the unarmed strikes with a use of your Hand of Healing, without spending ki points for the healing.
This gives us two instances of the healing.
We can use both instances on one creature.
There is no restriction on using the two instances of healing on the same creature. The important restriction to remember is that the affected creature must be within your reach. Hand of Healing requires that you touch the creature you are healing.