Bear with me through the obvious stuff.
Family relationships fall in to 3 categories:
- related by blood (mother, father, siblings, grandparents, etc.)
- related by marriage (spouse, step-parent, etc.)
- related by adoption, which can be formal or informal. Normally used only for nuclear family relationships, but I include other voluntary connections or associations for the purposes of this discussion.
In your family, you are related by blood to both of your parents, and all their ancestors. Because of your mother, you are related to your half-brother, and he to you.
Your "Jones" half-brother would be related to your father as step-son, because the "Smith" relationship (common-law marriage?) came 2nd. But you cannot say you are Mr. "Jones'" stepson because that marriage was already dissolved.
While not a given, most grandparents will acknowledge step-grandchildren, who are brought into the family through marriage. (In fact, obituaries don't always make the distinction, which complicates verifying counts of descendants). So, your "Jones" half-brother also has step-grandparents, because the "Smith" marriage came 2nd.
But any relationship you have with your half-brother's paternal relatives is not through marriage or blood, but only because of your half-brother. "Adoption" of children of a subsequent marriage into the family of a previous marriage does happen, although rare. There is no "official" name for these informal relationships between living persons, although individuals likely will use normal relationship words to each other.
In general, you have no relationship to your half-brother's relatives, the "Jones" family.