Actually, you’ve asked two different questions. In the title you chose for your question you asked “Is heaven achievable for everyone?” You then report that you asked a priest “Does everyone go to heaven?”
To the first question, the answer is “Yes.” God gives every single human being sufficient graces to enable that person to go to heaven if that person wants to go to heaven and chooses to cooperate with the graces God gives him.
To the second question, the answer is “Probably not,” although we cannot know with absolute certainty in this life if there are human souls in hell. (We do know that Satan and the other angelic demons are in hell.) God grants humans free will, and with that free will comes the possibility to choose to refuse the graces offered to achieve communion with God, the saints, and the angels in the next life.
