Remember that our OP is planning to buy a home. This means that the FICO scoring models that will be used are the much older "mortgage" models, not FICO 8. The available testing we have on the mortgage models is mixed, but there is a strong consensus that two of the three scores will get no help from the SSL technique. That said, it might help one, which conceivably could affect the middle score, thought it will also lower the AAoA.
The idea of each person adding a secured card seems (to me) very sound. I would make the minimum balance a bit higher than $2 personally, since there has been a few cases reported of $2 being reported as $0. $4 should be fine. If the credit limit turns out to be $200, that gives a wide range: $4.01 - $17.99.
As far as the idea of making sure the lender reviews and affirms all score related steps, that's a good idea in a way, though it will preclude using the SSL technique if that is something the OP wants to do. The lender will never have heard of it and will not be competent to assess its value. Bear in mind that the earliest you should expect to see the Alliant loan appearing would be Jan 19.
A large part of our OP's problem is that he and his wife have waited until a couple months before they plan to buy a house to begin planning for it from a credit perpsective. I am sure the OP realizes that so nobody here is beating him up about it, but it is still worth emphasizing for anyone else reading the thread, as a takeaway lesson.
