Plumbing – Low water pressure in house

It appears to me you are building pressure using the bladder tanks. Once the pressure reserved in those tanks is depleted your pressure drops because the flow is restricted (possibly ahead of those tanks). I would agree with Justin that you have a restriction that is reducing the flow and after the bladder tanks are depleted you are only getting the flow through the main line.

The fact that it takes longer to fill the sink with pure cold water tells me your problem is a restriction in the line feeding the water heaters and the bladder tanks are compensating for this somewhat when you fill the sink with pure hot water.

Look for a restriction in your main cold water feed line, and then at other points in the system. Check the air pressure in your bladder tanks with the line drained. Lastly, the piping looks too small to me. I would upsize that piping for better flow.

There is a restriction, somewhere. You could use your gauge to verify that the pressure (while you are flowing from faucets) at the water heater is good (you've only done so qualitatively so far, and you have means to test it quantitatively, so....) But basically somewhere in the line is something that is restricting water flow - perhaps a clogged or under-sized tempering valve (if there is a tempering valve) or the one I keep mentioning because it was a bear to track down and semi-unbeliveable when I did, an elbow almost completely plugged with solder. Could also be pipes plugged with mineral deposits.

If you open the hot faucets and pressure at the water heater stays good, move the pressure test up the line - somewhere it will get worse, and between there and the last place it was good is the problem.

Incidentally, 95 PSI is on the high side for many fixtures - you might want to add (or adjust if there is one) a pressure reducing valve and get to down to 75-80 PSI MAX.