I do see the faint lines on all three of those cassette tests. If the lines are getting lighter, I think the best thing thing would be to ask your doctor if they can run some bloodwork to look at your hCG.
I have gotten faint lines on cassette tests before, rushed in for bloodwork, only to find that hCG was basically zero. In fact, the same thing has even happened to me with FRERs. My fertility NP had no explanation for it, she said it's likely just an artifact of the test (eg evap line or indent). That may be what's going on in this case, but it is really hard to tell without bloodwork.
On the other hand, when lines show faintly and then begin to fade, it can sadly also be an indication of a chemical pregnancy. If this is the case, I am so so sorry. The symptoms of a chemical are faint pregnancy test lines that gradually fade, and a late period.
I attached some pics of my June 2015 chemical below. I was using Wondfos that cycle, and only had visible lines for two days before the lines started to fade.