I don't know much about half beaks. I know there are a couple of species sold under that name; that they are livebearers and are sexed the same way as guppies; and that males can be aggressive.
I looked on seriouslyfish - they just have one fish under the name halfbeak, Dermogenys pusilla.
Can be kept with similarly-sized, peaceful species that enjoy the same water conditions. In a freshwater tank good choices include other livebearers, smaller rainbowfish and freshwater gobies. Don’t keep it with any much larger or more aggressive species, as it can become shy and will be easily outcompeted for food.
It can be kept in groups and will usually be less skittish when maintained in this way. Males will often spar with one another, but lasting physical damage is rarely done unless space is very restricted. It is best to keep either a single male specimen or several in order to disperse the aggression.
I would have a look on seriouslyfish and see if the pics look like the fish you have, then see if yours have a gonopodium or normal anal fin. If you do have a male, or perhaps more than one male, that could be the problem with the guppies - which are quite a fragile fish at the best of times.
If the halfbeaks are the problem you will have to decide which you'd rather have, halfbeaks or guppies.
