We measured a sampling of these jeans of different waist sizes and lengths and find they are much like other jeans you’d buy these days. They are just a bit “vanity” sized in the waist. Across the size run, the actual measured waist band is just about 1” larger than the stated size, which is typical vanity sizing. So my primary advice would be to buy the waist size you normally wear in jeans; you’ll likely find a fit. The jeans include armor in the hips and knees. The armor units don’t make a difference in the size choice of jeans..
If you aren’t sure whether your jeans are vanity sized like I’m describing, then use a tape and measure around your waist where your normal jeans ride or measure the waist band of your favorite pair of jeans to verify. You’ll likely find that your waist and also the waist band of your favorite jeans measures out a couple inches bigger than the jean’s stated size. If so, you will be on track following my advice.
The inseam lengths measured out to be average. In the smaller jeans, the inseam of about 32”, the mid-sized jeans were about 33” and the larger jeans topped out at about 34” which is pretty standard. The pant legs are a simple design and could be hemmed. The knee armor position is highly adjustable, so even if you hem them or roll them up, you should be able to adjust the armor position to work.