The reason people think multiple GFCIs is odd, is this: A GFCI device (receptacle, deadfront or breaker) can protect additional outlets beyond itself. This is done by using the
LOAD terminals. On a GFCI deadfront or breaker, using those terminals is essential. However on a GFCI receptacle device, the
LOAD terminals are a constant source of misconfiguration by novices, handymen, ahem drywallers etc. Either they miswire it so it constantly trips, or they accidentally GFCI-protect outlets they were not expecting to, resulting in nuisance trips and surprise outages. So there is a warning tape across the terminals, that says in as many words, "Do Not Use: For Wizards Only".
Don't get me wrong, in a perfect world everything would be GFCI protected and every load that trips a GFCI would be fixed, and technical acumen and money would flow unlimited to get this done. However, in reality the technical acumen or time just isn't there, and the dangling problem isn't particularly serious. Compromises must be made.
So... multiple GFCIs on a circuit are appropriate when the installer realizes he is not a wizard; or; when there are downline loads which should not be GFCI protected for one reason or another. There's no way to protect half a downline. The apocryphal example is where receptacles are wired panel-1-2-3-4, with countertop receptacles in 1-2-3 and a refrigerator is plugged into 4 and it trips GFCIs. I don't care: A grounded refrigerator is the exact opposite of the use case for a GFCI, being a grounded metal box with all the electrical bits in the bottom back, shielded and beyond arm's reach for a human, and you are unlikely to drop a refrigerator in the sink.
In such a case, the
LOAD terminals will not be used at all.
Your direct problem
First you need to test. Since your devices are tripping both the Breaker (which looks for excessive current hot-neutral or hot-ground) and the GFCI (which looks for any current other than hot-neutral), the common factor is hot-ground, and current must be very high (bolted). An ohmmeter should measure this resistance out at near zero, and it would trip a plain breaker on any circuit. By the way, for that to happen, the appliance would need to have 3-prong sockets. If 2-prong, don't bother with this test:
I would first measure hot-ground with an ohmmeter and look for numbers that are too low (less than 5 ohms). Then try them on other circuits, particularly a non-GFCI such as the electrician's socket (if present) at your electrical panel since it's least likely to break anything else. Also, I would try it in your bathroom's GFCI. If it fails there, it's the appliances. If it does not fail...
I think your problem is one of two things: either the
LOAD terminals were in fact used, and misused; or more likely you have a grounded metal box and the wire attachment screws of the GFCI (perhaps the
LOAD neutral screw) is touching the metal box. If the back connections were used and the wire is pulling out of the back connections and touching the metal box, I've had that happen. Maybe it happpens when you plug the appliance in because you are flexing the box. Regardless, make a few wraps of electrical tape around the GFCI to cover the side screws. That is a good practice on any receptacle.