In this case, what if the inaction would cause harm to one or the other?

Harm done is not a consideration of the situation. In this situation it is still a case where one person wants something to happen, and the other one does not.

The view looks at these two people as a decision making system itself, and the lack of agreement turns the decision making system into one which cannot make decisions. As a result, it acts more like a leaf than as two people, where any action to upset the balance is immoral.

Remember, also, that this is from the view of a system with only those two people. From the view of society then it is absolutely true that one person coming to harm would be something society would want to stop, and such an action would be immoral. However, from the view within only that system, there are only two actors, and they do not agree with one another, so no choice will be made, and as such, the system will be treated as if it can make no choices.

The system would have to find a way of balancing the wants and needs one the two moral agents with one another.

I assume it cannot. If it can, then it once again becomes a decision making system, and the decision it makes is moral. Again, from the view of only the two people in that system. I did give the example of a massive guy beating on a little guy until things go the massive guy's way as a "moral" action of such a system, after all. Not typically what one sees as moral, but rarely do we look at morality in such a limited scope.

However, I'm not 100% clear on your notions that all actions are subjectively moral because all immoral actions don't occur. What do you mean by that?

That was me more extrapolating on the definition than trying to make statements about if something is moral or immoral. Pushing the boundaries, so to say. Specifically thinking about what happens if you define the scope of moral consideration to be "the entire universe".

If morality is defined by the "choices of the internal state of a system" and you pick "the system" to be "the universe" than all actions are moral, as they are actions within the scope of the universe. In such a case, the only way for an action to be immoral is if that action does not occur at all, as if it does occur in the universe, it is moral, and if it occurs, it occurs in the universe.

Perhaps, instead, it may be better to say that actions in a system are not applicable to morality. A system can only act morally when effecting, or being effected by, external systems. In that case you couldn't define "the universe" to be the scope, and it would fix that odd idea.

Or, perhaps it is that the universe, as it cannot act, or be acted upon by another, cannot be considered a moral actor in any form. Which would fix the solution in a way that is a bit less destructive to what I laid out.

Similar to above, what happens when your actions and inaction have consequences?

Those consequences do not matter unless they are in the scope of the system you are considering. If they are in that scope, then the consequences are "considered" when the system makes it's choice and an outcome occurs.

At that point you can't simply abstain from acting since both acting and not acting will cause (let's say) harm to one person in one case and another person in another case.

Remember that a subjective moral choice is the decision of a system, as defined. If the system involves two actors, one who is harmed by inaction, and one who is not, then it is still true that whatever that system decides to do is the moral choice. If it is the person who is not harmed by inaction forcing inaction, or the person harmed by inaction forcing action, doesn't matter, the action that occurs is the action which is moral, from the view of that system only.

Again, change your scope, and you may find that the addition of that scope changes the results of the decision.

If the scope is only those two (who disagree), then the entity is not considered to have any form of conscious thought or cohesion. If the scope changes to society (a group of people under a rule of law, a consistent moral direction), for example, a conscious direction will appear again, and that direction may dictate that society would not allow that to happen should it have the option to change it, making the action immoral from that viewpoint.

I think the aim is objective in regards to the scope of humanity (drawing the box around humanity, so to speak).

I would consider humanity to have this be less true, but for nations and such it is certainly true. There are some things were it is always true, but I think human interactions, across the board, are too complex and convoluted to say much that is definite about them.

But what do I mean by "objective." I mean that there exists an aim that we all aim at by default and without the need for argument for it, or against another. For me, that aim is human well being. In that sense, there exists an objective aim.

If that aim is broadly defined as "humanity aims to have all it's actions be towards well being of some form", then I can agree, but the massive numbers of wars, fighting, psychopaths, and so on, clearly show that not all humans are concerned with total human wellbeing.

As to the points:

1) It depends on your definition of well being. Is it "actions that cause at least one individual to be happy", or is it "actions which cause the most individuals to be happy", or "actions which cause happiness without causing the opposite." (with happiness being utility, or satisfaction, or whatever). Only in the first place, "at least one individual gains well being from an action" will I agree with this point in total, for all humans.

2) Is making the same point as 1, or seems to be.

3) Is this a condition or a statement? If your first definition, the idea of well-being to be "only one individual" which allows harm to others in the case of psychopaths, then there is no real argument against it, because it is inherently true. However, if it is any of the latter, you can argue for a person to choose selfishness, or psychopathy.

4) I got nothing for this one.

First, let me give an example of a specific action that will increase well being: Me taking a breath right this very instant. No one suffers, I gain (ever so slightly)

You actually gain pretty majorly, as if you didn't breathe you would die.

Otherwise I don't have much to say. I agree with the idea that, if you limit your scope to human actions, then there are a set of things that are "moral", and a set of things that are "immoral", and those are inherently defined by the average considerations of the humans inside of humanity, and I agree entirely when you mention "draw the box around humanity" in why I agree with you as to why that is a true thing. I wouldn't necessarily call those things well being, but I agree with the concept otherwise.