The bandit's horses did not run off.

So yes, you are correct, there are two horses available for Lyrisa and Allereun and another horse to do with however you please. (You could even sell it in town for about 17 iL, give or take, as when selling things it usually at half the price of what it was bought for, Persuasion (haggling) making the price potentially higher or lower). Appraisal also helps as well for other goods.