I inherited three Epiphyllum oxypetalum from my late grandmother. They were near dead. I managed to save them (somewhat). They grow, but not quite looking as they should in the stems. I believe those stems should broaden to near three and one half inches normally, thick and leathery to touch. Instead they are very narrow still (one inch across on widest older newer growth) and flimsy near paper thin.
I used a commercial cactus mix with a mix of sand, organic matter, peat and perlite.
I hope this is not too acid. How can I get them looking the way they were on the days being with grandma?
It sounds as though you may need to do some pruning and restarting. According to Terry Hewitt, author of CACTI The New Plant Library next year’s flowers are normally produced on this year’s ripened stems. Pruning out the oldest (and often discoloured) of these stems from time to time will help to keep the plant more compact and manageable. He also says that when tall-growing columnar cacti run out of room to grow any further, it is time to think about cutting them back and starting again. The top piece can be re-rooted and the bottom will normally make several new shoots. As for planting soil, he recommends a compost of one-third grit, with the rest made up of peat, loam and a good base fertilizer.
For more detailed directions see the webpage of the Cactus & Succulent Society of America at:
https://www.cssainc.org/index.php?option=com_content&task=view&id=281&Itemid=212 Epiphyllum Cuttings