The first thing to say is no, no, no to a male and female siamese fighter! They will attack and quite likely kill each other. Male and females should only be in the same tank for a very short period when spawning, after careful conditioning and under strict supervision. If you had a huge, very heavily planted tank you might get away with it but not in something as small as 30 litres.
Biorbs are also very hard to stock because of the shape. They should have less fish that rectagular tanks as the amount of water exposed to air is very small. In the 30 litre biorb, I would keep only one siamese fighting fish, either male or female, and maybe a snail for company.
Your 18 x 12 x 12 tank works out at 42 litres. I hate to tell you this but it is not suitable for the fish you have in there.
It is too small for for everything except the platies, and even then it is the smallest size platies should be kept in; and if you have the correct numbers of the shoaling fish (the tetras and danios need to be in groups of at least 6 each) and just one platy and swordtail then your stocking level would be at 200% - and that is going by the over-generous community creator on this site. With more platies & swordtails it would be even worse.
I know that neons and danios look small but they are vigorous swimmers that need longer tanks than yours. Some people go as far as to say that danios must be kept in tanks at least 4 feet long.
I'm afraid that your rectangular tank is only suitable for very small fish such as ember tetras and pygmy corydoras if your water is soft and acidic, or endlers livebearers if it is hard and alkaline.
Sorry to be the bearer of bad news.
