The legislative branch, for Locke, is said to be "the supreme power in every commonwealth" (265). The "first and fundamental" positive law is that establishing a legislature, which is in all of its actions to be governed by the "first and fundamental" natural law, which requires "the preservation of the society, and (as far as will consist with the public good) of every person in it" (264). On the next page he talks about this fundamental law as being the "preservation of mankind." This is interesting in that, as you recall, his earlier statement of the "first, and fundamental" law of nature is "seek peace, and follow it" (210). What Locke in the latter passage asserts as fundamental, he in the earlier passage treats as derivative (the second law of nature is "that a man be willing, when others are so too, as far forth, as for peace, and defence of himself as he shall think it necessary, to lay down this right to all things; and be contented with so much liberty against other men, as he would allow other men against himself"). I'm not sure that this inconsistency actually presents any challenge to his political doctrine; yet, if you're going to take the trouble to put your laws in a hierarchy, you could at least be consistent about it.
If there is a tension between the two formulations, it lies in the difference in priority between individual and commonwealth. In the latter presentation, the government clearly has the authority to demand the lives of some of its citizens, i.e. as soldiers, where this is necessary for the commonwealth as a whole. Such a demand could also be defended on the earlier order of presentation, but it presents itself as decidedly more problematic.
Aside from this, most of what he says on the extent of legislative power strikes me as fairly straightforward. There's a nice summary at p.268: the law must be promulgated, it must aim at the common good, it cannot deprive people of property without consent, and this authority cannot be transfered to any body besides that instituted by the citizenry.
If there's a problem with anything here, it's with the vagueness of the "common good," a notion he also invokes to help distinguish between a king and a tyrant (271). What do we do when large sections of the public disagree about what constitutes the common good? I'm not sure that Locke has a good answer.
In the next section, as a concession to "human frailty," Locke argues that enforcement of the law should be delegated to a separate branch of government, so that the legislators are not tempted to abuse their powers and place themselves above the law. I recall Locke saying something about a judiciary, and viewing it as a sort of sub-branch of one of these two--but I can't find the passage just now. The name he proposes for the third branch that he does mention is the "federative." The thought is that, although citizens have exited the state of nature with respect to one another when joining together to form a commonwealth, nevertheless, that commonwealth remains in the state of nature with respect to other commonwealths (269). The federative branch, then, is in charge of the international affairs consequent.
Interestingly, although Locke advocates for a division of power, he is decidedly not promoting a republican system of checks and balances of the sort briefly in place in Rome and later instated by the framers of the American Constitution. The legislative represents the majority, and its will goes unchecked.
The remaining sections of the Treatise deal with the charged issues pertaining to the recourse of a citizenry when the government violates its fiduciary trust. Significantly, Locke does not speak of a "right to revolt." Instead he speaks of a government "dissolving itself," and hence generating the imperative, per natural law, that a proper government be re-instituted. It is the tyrant, properly speaking, who is the true rebel, for he has violated the trust of the people (277).
There are essentially three ways that the government might dissolve and so need to be replaced. First, if the society is invaded and conquered from outside (272). Secondly, the government dissolves if the legislative is altered from that put into place by the people (Locke catalogs five different ways that this can happen (273-275)). Thirdly, when the legislative or executive branch acts contrary to the people's trust (275). It seems to me that the third category ought to capture everything from the second category and more, so I'm not sure Locke even needs the former. In any case, I take the basic point of this section to be fairly straightforward. Do let me know if you find anything valuable in his more detailed discussion of what these forms of dissolution look like in practice.
As usual, sorry it took so long to pull this together. I look forward to your comments.