Can I force someone to testify?

Yes.

 

The judge must help you if you ask. The judge will issue a subpoena to compel the attendance of any witness you need.

 

No one can avoid attending a trial as a witness if they are served a subpoena.

 

If a witness ignores a subpoena the judge can order the police to pick them up and hold them in jail until the trial and then bring them out to testify.