That "free money" is just enough to subsist on and pull themselves up by their own bootstraps. Instead of "choosing not to work", think of it as "seeking work that's a good fit for them". The incentives are set up so that entering the labor market and improving their earnings makes them better off - which, incredibly enough, most poverty alleviation programs (which are a non-trivial chunk of all government spending) utterly fail at.

> see if its worth the second earner working or if they make more just staying home

The available experimental outcomes show that by and large, people that stay at home on a properly-designed UBI are those who can thereby make highly-valued contributions to the household, such as by raising young kids. Otherwise, they choose to work just as much.