I have this list of vintage porn movies with nice plots [ mom son ]. All the new ones got step family scenarios which I am not interested. If anyone knows anything more please share.

1. Taboo series(1-5)
2. Taboo American style series(1-4)
3. Beyond Taboo 1984
4. Love to mother 1984
5. Maid in Manhattan 1984
6. Pretty Peaches 1978
7. Oriental Hawaii 1982
8. AWOL 1973
9. I've Never Done This Before! (1986)
10. Letters of love 1985
11. Shocking 1976
12. Wet wilderness 1975
13. The final Sin 1977
14. My sinful life 1983
15. Little Muffy Johnson 1985
16. Mother's wishes 1973 or 71
17. My Mother... My Brother... and I(1973)
18. The Last Taboo 1985
19. Joe Rock Superstar 1973
20. Sweet Young Sins 1976
21. Tracy in heaven 1985
22. Momma's boy 1984 or 85
23. Sunny 1979
24. A girl's best friend 1981
25. Platos the movie 1980
26. The final test 1978
27. Sex and Astrology (1971)
28. Black Taboo 1984
29. The New Neighbours 2006 [might be step - not sure]

Note:  This is not limited to vintage ones, if you know any new age movies with good plot, feel free to share [ but no step family scenarios] 

Cheers!