Hi and welcome to the forum
I can't see any white spot on the unusual pleco, but its fins are a bit clamped, which could be poor water quality or a disease.
I can't tell anything about the bristlenose pleco because the fish isn't in focus. If you post a decent picture it might offer more information. Check pictures on your computer to make sure they are in focus before uploading here.
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How long has the tank been set up for?
What is the ammonia, nitrite, nitrate and pH of the water?
What sort of filter is on the tank?
How often and how do you clean the filter?
How often do you do water changes and how much do you change?
Do you gravel clean the substrate when you do a water change?
Do you dechlorinate the new water before adding it to the aquarium?
You can ask your friend with the goldfish these same questions. We might be able to work out why their fish died.
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If you think it has white spot, do a 75-90% water change and gravel clean the substrate. Clean the filter too. Then raise the water temperature to 30C (86F) and keep it there for 2 weeks, or at least 1 week after all the white dots have gone.
Make sure any new water is free of chlorine/ chloramine before it's added to the tank.
Filters should be cleaned at least once a month. However, if the filter is less than 6 weeks old, do not clean it. Wash the filter materials/ media in a bucket of tank water and re-use the media. Tip the bucket of dirty water on the garden/ lawn. Cleaning the filter means less gunk and cleaner water with fewer pathogens.
Increase surface turbulence/ aeration to maximise the dissolved oxygen in the water.