Step-son is getting married...what is the proper etiquette for the step-mom?

I am going nuts about this up coming wedding. My step-son is getting married and his future wife's parents are planning everything and basically paying for everything too. I am married to my step-son's Dad, however, my step-son's mom did not remarry. What is the proper wedding etiquette with respect to sitting in the Church and especially at the reception. I have mentioned to my husband that I best be sitting at the front table at the reception with you and your ex-wife or else all hell is going to break loose. My husband said that its not up to me, and said like hell its not, its called sticking up for your wife! In my opinion, as a step-mom, I should not be discriminated against or have to take two-steps back and let my husband sit and hang around his ex-wife all day while I am left in the dark. I am a part of this family now and should be treated fairly. Responses??