Some Advice (Long post)

I had my son towards the end of what was suppose to be my last semester of college. But I had to come back this fall semester to finish so I had to leave my son with my parents. So my brother and his wife just got out of the air force and moved in with my parents until they find they're own place. They have two kids, one is four and one is two. My son recently started to stand up while holding on to a table or couch. So my sister in law has taken it upon her to hold his hands and encourage him take steps. I'm pissed about it because I already had to miss so much to finish my degree (only one more month to go ) and I told my mom to tell my sister-in-law to stop doing it. My mom didn't say anything so I told her I will curse everyone out if when I get home my son is already walking. So my mom told me that she just won't tell me if he starts walking. Like tf is wrong with her and my sister-in-law? They know it killed me when I missed him crawling for the first time so why are they trying to teach my child how to walk? I'll literally be home for fall break in a week. My sister-in-law should focus on potty training her two year old instead of trying to play mommy with my son. I'm so pissed. I want to go home and slap the shit out of her!! Ugh!!! I'm also hurt because my mom isn't on my side even tho she promised me that this wasn't going to happen. My child was not attempting to walk until my sister-in-law intervene. Why can't they back off and understand where I'm coming? How do I make them understand? How do I make them stop? I'm so pissed and heartbroken right now. Sorry for this being so long.