You are asking the wrong question-you don't really care what this maximum is since you know to hire a lawyer. Get a VERY experienced DWI attorney in both states and pay all the money you can find to avoid the worst. Its time to do some serious rehab and DWI education that you won't find in prison.
To answer your question directly, the minimum sentence for a 3rd Degree Felony in Texas is 2 years in prison, and the maximum is 10 years. Assuming the worst, that your father-in-law's probation will actually be revoked and that he is sentenced to prison, he will be eligible for release from prison on parole when the actual number of days he serves (his "calendar time") plus any credit for good conduct in jail/prison (his "good time") equals one-fourth of his imposed sentence.
Please note that eligibility for parole does NOT mean that parole will be granted. Roughly speaking, though, at least on his Texas case, your father-in-law is looking at about 6 months to 2 1/2 years of actual incarceration, IF (I say again) IF his probation is revoked and he is granted parole at the earliest possible date of eligibility.
However, given the length of time that he did spend on probation, and if there are no other violations over the past 10 years, the court here could continue and discharge him from probation and just let him deal with the new charges. There are a lot of variables that would go into that.
Maximum is 10 years. Minimum is 2 if sentenced to prison. You need a local lawyer familiar with felonies and DWI's.
My answers are intended only as general legal advice and are not intended to create an attorney-client relationship. There is no substitute for a full consultation with a local experienced criminal defense attorney. For more answers based on my 19 years of experience visit my website, www.austincriminaldefenseattorney.com
Mitigation is a key factor in your loved-one's case. Why did the Texas prosecutor file a motion to revoke probation? What are the allegations being used to support the revocation? What things can your father-in-law be doing to appease the Texas prosecutor and judge? These are questions only an experienced criminal defense lawyer in that jursidiction can answer. I'd consult with one immediately. There may be ways to improve your father-in-law's position like paying delinquent fees, finishing community service, completing any required counseling, and the like. Again, only a good defense lawyer can help you evaluate these options to help eliminate or reduce the possibility of recieving the maximum penalty in this important matter.
Let me add that whatever the original sentence, the judge has the authority to reduce it if the probation is revoked. What I mean by this is that even if the sentence was 10 years suspended for 10 years at the start, the court has the authority to reduce it to 2 years, or 4, or 9, or whatever between 2 and 10 if the probation is revoked.
Answers on Avvo are for general information purposes only and should not be relied upon as legal advice. No attorney / client relationship is created by providing this answer. For specific advice about your situation, you should consult a competent attorney of your choosing.