Can joint suspension be reinstated?

Can't say specifically. If you can show you did not know perhaps the judge will not violate you. If you are violated, technically, the judge must lift the stay and impose the 6 year term. You may be able to negotiate around this, however. I will also say that most people confuse a "stayed" term with a "suspended" term. They are very different but it is common for non-lawyers to use the common term of "joint suspended" for both. Hopefully, you have a suspended sentence which gives the judge a little more discretion.

When you are on a joint sentence you are on probation. If you violate your probation you can have it revoked and be placed in state prison for the amount of time that was suspended. With the problem you stated you have two possible paths for the DA to take. This incident could be charged as a probation violation and you would have a probation violation hearing in front of the judge. This incident could be filed as a new case and tried before a jury. During both processes there will be offers from the DA or the judge. One offer maybe to reinstate you to your program. The chance of the outcome being one that you would like increases greatly if you are represented by an attorney.

CAN it be reinstated? Sure. WILL it? The honest answer is that no attorney can predict the outcome, nor even give an intelligent opinion, without reviewing and knowing all the charges, evidence, police reports, testimony, priors history, attitude of the DA and judge, etc. The outcome of the new felony charges is the primary issue, as sentencing for that will include the probation/parole violation or reinstatement at the same time. Of course I can help you can fight the criminal charges and get the best outcome possible. When arrested or charged with any crime, the proper questions are, can any evidence obtained in a test, search or confession be used against you, can you be convicted, and what can you do? Raise all appropriate defenses with whatever witnesses, evidence and sympathies are available for legal arguments, for evidence suppression or other motions, or for trial. If you don't know how to represent yourself effectively against an experienced prosecutor intending to convict, then hire an attorney that does, who will try to get a dismissal, diversion program, charge reduction, or other decent outcome through plea bargain, or take it to trial if appropriate.

You're on very shaky ground. You need to talk to your lawyer about this. If you don't have a lawyer anymore, ask the court to appoint the public defender when you go to court. Don't try to explain yourself to anyone but your lawyer.