Hi Abigail! Well, I may have something for you...it's not a home run, but it might be a good base hit, or maybe even a double.
I looked at Robert and Ethel Johnson on the 1930 Bosque Co. census just to get a feel for them. And of course I saw Leonard there. Interesting that they orginally had him listed as "friend" and then the enumerator wrote over that "lodger." Anyway, what REALLY interested me were the George W. and Mattie Johnson right above Robert. Sure looked like they could be Robert's parents: George was 74 and Mattie is 68 to Robert's 42. And George was born in AL.
So I tracked George back...and you are right that Leonard is NOT with Robert in 1920. No, he's with George and Mattie in Bosque Co. TX in 1920. There's a Leslie Pruette (11 yrs)and William L. (5 yrs) listed as adopted sons of George and Mattie.
I tracked back to 1910 and George and Mattie are in Bosque Co. with the youngest 3 of their 10 natural children. But get this, in 1900 they are in Lanette, Chambers Co. AL with all 10 of their children (Robert is actually James Robert). Small world, isn't it? (BTW, it is TREMENDOUSLY helpful and important to post the county; most records are by county, not town).
So here's my hypothesis: of the 10 children, there are 3 of the Johnson girls old enough to marry and have Leslie and Leonard. I'm thinking that perhaps the mother died and Leslie and Leonard went to live with their grandparents (because it is a bit of a stretch that these older folks send off to Alabama to take random orphans in their home in Texas). And by 1930 they re just too old to care for a teenager, so Leonard moves in with his uncle, who has children that age.
Now all of this is ONLY a guess. But there are a lot of coincidences! And there are some other possibilities, but I think this is the one to prove/disprove first.
I have all sorts of censuses etc. if you don't have access to them. Just post again and I will post them. Also, the family seems to stay in the Bosque Co. area...Robert dies in China Springs, which is in McLennan Co., in 1944. He's buried in Fairview Cemetery there. And the other Johnson brothers (Alonzo W. [Lon] and William H) are around as well.
Anyway, let me know if you want census info, etc. posted. I hope this helps some! Happy Hunting! (and I'm no relation, just a volunteer) Andrea P.S. From Robert's death certificate: Mattie's (his mother) name is Martha G. Turner. And the Johnson girls who might be William Leonard's mother are Annie C., b. 1883, Mary b. 1889, and Nannie P., b. 1891.