I agree i can speak passable spanish with my wife's family. i learnt exclusively on duolingo.
I don't know if its the best way but it kept me motivated to come back and put in some work in a fun environment. which i belive is the biggest problem to solve for any sort of learning.
The suggestion is that it's likely that you did much of your learning from speaking to your wife's family, with duolingo giving you a kickstart and the confidence to do so.
Having conversation partner(s) to practice with generally trumps any other learning method for languages.
I don't know if its the best way but it kept me motivated to come back and put in some work in a fun environment. which i belive is the biggest problem to solve for any sort of learning.