It may not be ideal, raeburter, but as long as you acclimate the betta first and watch to see that they are adapting ok, if it is something you want to try, or need to do, try it.
Watch the betta behavior, keep an eye on the water conditions, divide the two bettas and the guppies and try it. Like I said it's probably not ideal but it might work for now.
How's that for equivication?