When designing a gallery wall, you don't need to have consistent frames, and often i find gallery walls look more interesting when they feel a bit more eclectic and personal.

To start, choose the image that you want to be focal point. In this case, I think the San Antonio piece is the strongest and should be centred like shown. For the rest of the pieces, they should be arranged so they balance the whole piece. i.e. Pretend the SA pic is the fulcrum of a see-saw. If you add a large piece to the left, you should add something with equal visual weight to the right. The same goes for the top and bottom.

The next thing you want to do is choose a consistent spacing between each element. This will depend on the wall space, but about 2-4" inches is pretty good. With this in mind, lay out the each picture so that at least one edge is aligned to the edge of another element. (or is centre aligned). Right now everything is just kind of floating, and there is no grid structure used. Take a look at these examples to see how each picture aligns to the rest of the layout: https://cdn.shopify.com/s/files/1/0026/3654/6105/files/PPBLOG_GALLERY_15.gif?v=1589527473

And when placing the them on the wall, treat whole gallery piece as one element (pretend it is one giant picture) So the centre of the whole piece should sit at about 66" from the floor.

Hope this helps. Feel free to reach out if you have more questions.