The tank is to small for those fish to go together. I would suggest

1 betta
2 platies
1 cory catfish
or

1 bettas
3 cory catfish.

Also bettas do great with most other fish not including male guppies Last you need to have the at least 6 of the same type of rasboras for them to be happy.


Hope this helps

Even though its not true that bettas will kill all other fish an ignorant idea which wont go away a 30 liter tank is really an absolute minimum for keeping fish with them since its true that they are territorial and there needs to be space for all the fish. The smaller the tank gets the more likely the betta causes problems because the other fish cant get out of his space.

With bettas its extra important to keep schooling fish in schools. It would be best to go with 6 rasboras all the same kind. One type will look 10 times nicer than a hodgepodge mix anyway. Then you leave out the guppys and platys because there is no room and not a great choice anyway.

That sounds massively overstocked for a 30 liter tank. Your tank could fit the one betta but all your different fish require larger tanks than that.

In a 75 liter tank

1 betta
6 rasboras
5 platies

would do alright a guppys long fins are a target for bettas aggression. But in a 30 liter that is way too overstocked.