Step kid giving problems eating, anyone else?

Hello step moms out there!!! I have an important question!

My youngest stepson has for the past 3 years gives us problems eating, it’s been off an on, but it happens often. He will eat loads of food at his moms, but will force himself to puke our food and refuse to eat saying “he’s not hungry”

Remind you that he is going to be 10 years old in October and for example since Tuesday he’s only eaten 3 things and keeps saying his stomach hurts, but not hungry(always the case)

Every week he comes to our house my husband and I argue because we deal with this so often that it even affects my oldest stepson.

My youngest stepson admitted that his mother has been putting things into his head and we are all 100% sure she tells him to do this to cause problems in our household.

I’m recently pregnant and I don’t want this stress on me causing me to have another miscarriage.

I’m becoming to recent this child! Thinking of the weeks he comes to our house is just terrible because I know he will cause problems.

My oldest stepson lives with us full time because their mother is a full blown alcoholic and literally lets the youngest do as he pleases at her house (eat whenever he wants, go to sleep whenever he wants, tells him school isn’t important.. etc..)

Well we have rules, a bedtime and chores we have them do! It’s like it’s a control thing because we don’t let him do whatever he wants like at his mothers. It’s always a game with this kid. Constant “I want to live with you” NO “I want to live with my mom” blah blah blah always a different story! He lies exactly like his mother ALL the time!

Please help if you ever have had this and what has helped!!!