No, definitly not. The pleco, for one thing, will be far too large, and the pleco needs a 30 gallon tank minumum just for itself.
As for the betta and guppies, they would FIT in the tank, but they can't coexist together. The betta will see the guppies as a threat, and attack them.
I'd just get either the ONE betta male, or the guppies. Sorry for the disappointment!