convert only the tif files in a folder with also dng

You could use Bridge, with view of subfolder content on, with dng file filter off + running a Batch or Image Processor or Image Processor Pro scripts on selected files.

One script option here:

https://raw.githubusercontent.com/Paul-Riggott/PS-Scripts/master/Picture%20Processor.jsx

https://prepression.blogspot.com/2017/11/downloading-and-installing-adobe-scripts.html

Another script here:

https://www.marspremedia.com/software/photoshop/batch-multi-save

Or a custom script without a GUI could be created for this task.

In Photoshop, use Image Processor to convert your TIFFs to JPEGs in folders and subfolders. Go to File > Scripts > Image Processor. In the Image Processor dialog that opens, do the following:

1. In Step 1, select the folder and select the Include All sub-folders option. 
2. In Step 2, select the location where you want to save the converted files.
3. In Step 3, select Save as JPEG and enter the Quality level (leave the rest blank if you're not resizing the images).
4. You can skip Step 4 if you're not running any actions.