That is exactly the point OP is making. If you do not have a mandate to govern from the people, you need unanimity from all homeowners. Those are the alternatives.
You don't strictly need a mandate from the people; authoritarian governments can be legitimate despite not having such a mandate. However, it's an impossible trilemma: successful action needs at least one of unanimity (parent commenter's approach), threat of coercion (government), or tolerance of free-riding (charity).
If you require unanimity then everyone has veto power over every decision which is difficult to manage even with 40 people. If you select 5 or even 3 people out of that group of 40 then it become much easier to make a decision. If everyone can nominate and vote for their representatives then they should feel it is fair when they have to abide by their decisions. At such a small scale you have very direct access to your elected representatives so you should feel that they have heard everyone's opinions and will hopefully do their best to accommodate them and if they don't then you should not elect the same people again.
At this scale you really can't call it threat of coercion, the land isn't owned by a separate entity so individuals could choose not to participate and all participants have direct access as well as a significant weight to their vote. It is a self-binding agreement if you choose a representative.
In the case of the 40 people, if a few of them consider whatever proposal stupid they can ignore it (e.g. not pay their share of something).
If they organize a republican government and have 4 representatives, some of the citizens could still refuse to pay (even if they accepted at first the election of the Street Senators). Coercion is what makes, say, Rhode Island, different than that person's street because if a few Rhode Islanders decide property taxes are stupid and refuse to pay, eventually all their land will be confiscated and they'll be dragged off of it by armed police.
Define 'bind', please.
If my neighbourhood elects representatives who decide that we should all have black trash bins, then how am I 'bound to abide by their decision' if I want to put out a green bin instead?
The problem is moot if the decision is unanimous, since a unanimous decision has no dissent by definition. It comes back with any rule from authority, even if that authority is republican in nature. Note that I said coercion, which is broader than a simple threat of violence; shame and shunning are some of the oldest coercive tactics in the book.
Majoritarian government is great because it offers an easy path to legitimacy, overcoming the 'who died and made you leader?' problem. However, my argument speaks to the leader part of that question, not the you part.
Where do you think governments come from?
The oldest Epos we have, Gilgamesh (from the top of my head):
"We came early in the morning. Anyone opposing, we killed. We took everything.
...
until they learned it was better to submit to us."
The rest is how he became then a king, but got bored and now thought, might as well be a good king (but that too got booring, so he got onto adventures angering the gods).
So this is the founding mythos of Babylon. Often considered the root of civilisation.
" Gilgamesh is an asshole, a liability, but the text seems to know that."
Kind of? It is not really condemned I think. He is still their powerful (god)king and might is right. (So he had the right to be an asshole).