I agree - there are 7 aliyot, your shul may not give you all of them, but you should be entitled to a few. The bar mitzvah boy generally gets maftir (the last one).
Most fathers in my community (DL/MO) stand next to their son the whole time, as well. So your husband can be on the bimah while your son is reading the Torah.
Agreed that the father can be on the bimah the whole time.
This type of situation can happen if the family are kohanim or leviim. Then the father usually gets kohein or levi and the boy gets maftir. Actually, often the father gets no aliyah because the grandfather on that side gets it. So if this is the case, you do have a question, and I would say this:
I don't know the family situation, but if there is no specific reason for not having the father, I would give the brother hagbah or gelilah and them give him kohein or levi during minchah. And if he wants his brother up on the bimah with him too, he can do that. I am JPF/yeshivish (where they meet).