You'll need a image capture program which will allow you to pick and choose which frames from the videos you want to save as a JPEG.
The only good way of combining elements of various images is to make a composite. When making a composite, each element such as clouds from five different photos would be on their own layer. It's just like how an overhead projection works that you've may have seen in school. Think of it as pages of clear plastic where each page has certain elements that when stacked, the combined pages make on total image.
Photoshop, Gimp, Luminere, OnOne are but a few photo-editing programs that utilized layers. Some of these programs such as Gimp, are free for download. Gimp (gimp.org) is one of the more popular ones and as a result, you can find pretty much all the tutorials you'll ever need on YouTube. Do a search for blending, layers, and composites to help you create a really great image.
Once layered, you can then move or edit each element independent of the other parts of the whole image. This allows you to combine various elements and then blend them harmoniously into one composite image.
This can be rather difficult to do and it has to be done on a laptop/desktop; a phone will not have the ability to do this type of editing as the software simply doesn't exist.
One word of advise - when working on multiple layers you will need to save your work. You cannot save multi-layered images as a JPEG; it's simply not allowed. Therefore, save your multi-layered images as a TIF, then save it as a jpeg. When trying to save the work as a JPEG, you will get a warning that you must first flatten the multi-layered image into one single layer. At this point, the program that you use may give you the option to save the image as a flattened jpeg, or you'll have to go into the program, flatten it, and then save it as a JPEG. What you most certainly DO NOT want to do is skip the step where you save your multi-layered image as a TIF. Saving the image as TIF will allow you to go back at any time and fix anything on any layer. Once the image is flattened, saved and closed. You can never go back and un-flatten the image. So save it as a TIF then as JPEG.