Calling all Catholics and stepmoms

Tomorrow is my 8 year old step sons first communion. I am very close with him and have been since he was 3. He is being raised catholic but I am not catholic but I often go to church there. My husband and I are having a fight about if I am allowed to sit with my husband, step son and his mother during his first communion service and participate in the mass and be recognized as a parent with them. His mom is an alcoholic and actually even showed up drunk to the first communion-rehearsal today. She can be mean and violent. I spend more time with my step son than either of them because of my work schedule. I am religious and active at at Lutheran Church. My husband thinks I should just sit in the back by the grandparents while him and his ex wife sit with their son without me.