You have learned the hard way what many of us similarly learned. You had/have the wrong mix of fish in that they are not compatible. Advice from fish stores is unfortunately usually very inaccurate and misleading. So, before buying any fish, always research the species.
To work together in a community of more than one species, the fish must have thee same requirements when it comes to water parameters (GH and pH and temperature), the same requirement in aquascaping (substrate, wood, rock, plants may all be part of this), the same requirements with respect to filter current, the correct number if it is a shoaling species, and the correct inherent temperament to match the other fish. Research and experience teach us, and this forum is a great tool in that approach.
Angelfish and gourami are best not combined as they as so much alike in temperament--males are territorial, the degree depending upon the species and the individual fish.
Angelfish are shoaling fish requiring a group of at least five to avoid internal aggression related to their territoriality and temperament. Two fish usually will not last long before one is dead, unless they are a pair (male/female) that have accepted each other and bonded. I can explain this more if asked.
Rams have the same issues as the angelfish, so here again a bonded pair or a small group (space can make this impossible though) or a solitary ram.
Tetras are shoaling fish that need a group, usually six or seven is suggested as minimum but more will always improve things for the fish, and some need more to begin with. When this is denied them, because they "expect" it and it is programmed into their DNA, they frequently turn aggressive out of sheer frustration. Having long-fin fish or sedate fish--the angelfish and gourami and ram all fit this--in the tank is just asking for trouble from these fish. Matching suitable small shoaling fish with angelfish, gourami or rams takes some effort. The advice you got elsewhere was inaccurate.
Just to be certain, if you could post the fish you are keeping after the others are removed (if you do that as mentioned previously), along with your water parameters (GH and pH especially), we can undoubtedly find suitable fish to consider.