First you need to segment the image to find all the "red" regions. I have some demos for color segmentation in my File Exchange. Or you could use the Color Thresholder app on the apps tab of the tool ribbon.
Once you have a mask of the red regions, you can ask regionprops() for the centroids.
Then, with the centroids, you can use pdist2(), in the Statistics and Machine Learning Toolbox, to find the distance of every blob to every other blob.