The economic issue here is a positive externality.
If both people are working 40 hours, and they get an 80-hour house, and Brian is happy with that, then that means the marginal benefit to additional hours of work matches the marginal disutility to Brian of working any more hours for a larger house.
Extra work by Brian is not worth extra house. He stops there.
But if Brian stops there, and Angie has a different choice? If Angie puts in another 10 hours voluntarily, because she’s “comfortable” doing so? (This seems to be the implication of Option 1.) She does this because she thinks it is still worth her own while, even though Brian isn’t helping out with it.
Then that means the 41st hour of labor is worth the 81st unit of house to Angie (which also, marginally, benefits Brian but not enough for him to put in the effort by himself). Then the 42nd hour of labor is worth the 82nd unit of house for Angie, and so on. That continues until the 50th hour of labor to Angie is personally worth the 90th unit of house. She would be “comfortable” putting that work in on her own, even with Brian staying at 40 hours.
But that information (if I continue to interpret Option 1 in this fashion) rules out option 4 entirely. There’s almost no way Option 4 could be optimal for the two of them together. (The exception is constant marginal benefit, which seems unlikely.)
Angie was willing to put in 50 hours of labor to get 90 units of house. She was “comfortable” with that, according to Option 1. (That doesn’t mean she’s happy that Brian isn’t helping out. Just that she would do it, if she had to.) This is to say that the added benefit of the 90th unit is worth the 50th hour of labor.
But then Option 4 doesn’t make any sense.
If Angie already has a house 90 units large, and she would’ve put 50 hours of effort into getting that by her own efforts, but she has only put in 45 hours of labor so far (and the 46th through 50th hours of labor are progressively more stressful than the 45th, which is generally the case), then the marginal effort to Angie of more labor is still worthwhile to her to get an even bigger house to enjoy, even if Brian stops at 45 hours.
Solving the positive externality here involves asymmetrical efforts.
Brian puts in more than his 40 optimal hours. Why? Because he’s enjoying the extra house, too (just not as much as Angie). If we were solving this as a system of equations, then Brian’s extra effort needs to balance the extra house that he gets from Angie’s extra-extra-extra efforts. He’s willing to put in a few extra hours, because she absolutely lurves big house. And she’s willing to put in these efforts above and beyond what he is, because she values the extra house more highly than he does. But him helping out a bit beyond his comfort level is what makes the deal work.
If we could specify utility functions, then we could find the exact optimal point of effort for them both.
That’s probably not necessary here.
But what “should” happen (if they’re acting “optimally” according to the scenario as I am currently interpreting it) is that the person who wants more house should work more than the other partner, and the other partner should also put in a bit more effort, beyond what he would do on his own, in order to “pay back” the extra-extra-extra benefits from the other person that he’s receiving.
Both benefit from asymmetrical efforts more than they would from equal efforts, if they can make the deal work.