- A tube does not have an air pressure maximum - it is restrained by the tyre and rim (*1)
- A tyre does have an air pressure maximum
- A wheel/rim has a weight maximum but not an air pressure maximum (*2)
So your combined system weight is going to be about ~260 pounds (120 kg) by the time you include the bike, the panniers, the rider, and contents of your pockets/bottle.
Most conventional bikes have about a 40:60 split, so 40% of your weight is on the front and the rest is on the rear. This changes when braking or accelerating, or if you've bounced through a pothole. Upshot, your front wheel is holding about 104 pounds (48kg) and the rear is about 156 pounds (71 kg).
At 65 PSI in each tube, your front wheel will have a contact patch of 1 3/5 square inches, and the rear will be 2 2/5 square inches. This is the area of flattened rubber that touches the road to equalise the total mass.
Your 50mm (2 inch) tyre will compress by some amount to make that surface area. So the energy to deform that tyre initially comes from the weight, but to roll forward the energy comes from your pedalling and that's why big soft tyres feel sluggish.
To put that another way, a higher tyre pressure deforms less so saps less energy to roll. (*3)
The max and min width of tyre your rim can take depends on the inner rim width. There's a full Q&A on that subject here: What is the maximum or minimum tire width I can fit on my bicycle
Bike tyre measurements are not simple - there are a crazy number of systems where a bigger number can be smaller than a smaller number.
For your existing 50mm 26" tyres, you need a 50-559 (to use the ETRTO system) which is the same as a 50mm wide for a modern 26" rim. Just make sure you have a third tube as a spare.
Finally - I don't know where the 28mm figure comes from. Its possible you've seen something about modern road bike tyres whose widths have increased from 19mm to 23 to 25 to 28 on pro bikes, but these are for a different rim size and style of bike.
Remember, Amazon is not a bike shop.
They're just a box-mover who wants to sell stuff. If you need practical real useful advise, a Local Bike Shop/Store can be much more helpful. Or ask here on Bicycles.SE, or ask in [chat].
- yes a tube will eventually pop if inflated outside a tyre, that's not what I meant
- yes a rim/wheel will fail if the air pressure is too high AND the rim is worn
- to a point - there's a sweet spot in pressure, where too much has no grip. We want the goldilocks pressure for each wheel and conditions.