Is it just me

Good morning everyone so for the past couple of months I’ve been having issues with my so’s kids he has a 3 year old & a soon to be 11 year old. Some times when he has them they run the household the 3 year old throw temper tantrums, hits, & screams when he does not get his way & then the 11 year old acts like the chucky doll (don’t know how else to describe his behavior) when his dad goes to the store to pick up some things for dinner or just in general... his barely shows his face when his dad is home but as soon as he leaves he comes out of his room and starts harassing me... demanding that I get him food or demanding me to do things in general.... I had to tell him one day “I’m not your one of your friends i respect you & your space I need you to do the same thing for me”...a couple of days ago I asked the 11 year old to stop jumping on the couches he proceeds to say “you can’t tell me what to do” I spoke to his dad about it his dad said he talked to him about it... the next day the little boy starts putting his fingers in my face & “accidentally” pokes me in my eye... I got so frustrated and isolated my self in the room until they left... this has been an issue for months he wasn’t like this before at all he was sweet & shy.. then his dad & I would buy him things & he refused to wear them. But when his mother would buy him the same exact things he would wear those & she only would buy them once she saw pictures of him in them... I vented to a friend about the issues I was having & she said it sounds like the mom is telling him to do those things... & I didn’t listen to her cause I’m like I don’t think a grown person would tell her child to act like that.... & as time went on I started to see what she was talking about... I had a talk with my so & told him if this keeps happening I’m going to have to separate myself from the situation... I don’t discipline other people’s kids... I don’t yell at them I don’t do any of that to keep down on confusion because I know his ex does not like me... but she claims she does.. but runs back and tells lies about me... how do you guys think I should go about the situation.. it’s an on going issue that’s causing issues ...