This member was banned before the question was answered. In the interest of not having unanswered questions on the forum...
Step 1: Create a new master image (File > New), with a canvas of desired size, with a black background.
Step 2: Copy each photo into a new layer on this new canvas. (CTRL+A on the image to select, go to new image, CTRL+V to paste. Substitute CTRL for APPLE on Macs.)
Step 3: Use the Free Transform filter (Edit > Free Transform) on each layer, resize as needed.
Step 4: You can merge the individual image layers by holding CTRL and selecting each photo layer (but not the background), then using CTRL+E to merge the layers. Then use the "dotted box" selection tool (I forget the name of it) to clean up the edges of the now-single resized photos layer, and create a smooth/clean identical edge for all images by deleting the outer edges. You'll be selecting the part of the image you DO NOT want to keep (the background will stay), and deleting it. If this step doesn't make sense, simply reply to the post, and some images can be provided to expanded this mini-guide post. This can be done in several ways, including using square brushes or layer-based crop with guides, but I tend to take the path of least resistance.
Easy and basic task here.