I wonder why the charge is third degree felony IF the person has no priors. Assault causing bodily injury (not serious bodily injury nor assault with a deadly weapon) on anyone including a family member is a Class A misdemeanor UNLESS the person has a prior offense of assault on a family member and the new case involves a family member. If so, THEN the charge is a third degree felony assault on a family member.
The potential sentence is 2 to 10 years in prison and / or a fine. Whether or not the State will consider offering a deferred adjudication probation or straight probation depends very much on the facts of the case, and possibly on the facts and timing of the prior case (which I assume must exist.)
There is no "average" sentence. It is on a case-by-case basis.
I suggest you hire a good local criminal lawyer.