Images within Posts Size Issues

I am trying to show 260×260 thumbnails 3 across and 2 deep inside each post. I’ve tried the gallery insert but it makes the thumbnails super tiny, I tried using customized div tags and the code is ignored and leaves the thumbnails tiny. If I post the images directly in using the “medium” setting they overlap.

Is there any solution to making a nice 3 row with larger square thumbnails?

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