You can also check with the local child protection offices for a list of professional supervisors. I know there are issues with that office for you but they do have the list. You might also ask your therapist for advice about this. If at all possible, get the courts to assign a supervisor to the case. The supervisor is supposed to sit back but in the room with you and watch and report to the court on how things go.
If they will allow you you to have the visits at your home, it is best. Then you are in a familiar environment and have all the things that you need at hand. I don't remember how old your kids are, but be sure to have appropriate healthy snacks, changes of shoes and clothing, car seats if needed and even diapers and wipes. Don't expect your ex to provide anything for the kids. Just that they are clean and on time. You will look better if you are prepared ahead of time. I have been a supervisor for visits and these are things that I recommend.