Using mask for different products, problems with geo-code and graph builder

Hello everybody,

i am working with Snap to create Temperature Images from Landsat Images. For this, i use NDVI Values to estimate LSE. Because the NDVI isn’t really accurate to distinguish between Water and City sometimes, i’ve made a water mask. I want to use this water mask for all of my images, so therefore they all have to have the same extend i’ve learned. I have 38 images from Landsat 5 and 8, wich i all individually subsetted, so they do not have exactly the same extend. I’ve now learned about the graph builder and that i could have subsetted all images with this tool to the same extend. So i tried this, but i cannot choose a source band.

I just cannot click or do anything with this box. I wanted to try collocate, but there first was an error, that some of my subsets are not geo-coded. It seems that this fits to the Landsat 8 Subsets, landsat 5 is fine. Why could this be? (I see geocordinates when moving over the image, so i don’t understand where the Problem is here.
So i collocated only the Landsat 5 images, wich worked, but is not exactly what i want. I do not want all Products in one, but all Products in one extend, so i can use the water mask for all of them. What would be the best way to do this? And do i also need to resample the products first, to go on and use the mask in the band maths calculator?

Your help is really appreciated, thanks in advance!