Severe Safety Concerns

Its not really pregnancy related but i may be over reacting a bit, my partners 5yr old son continues to try get between us, we cant shower together hell i cant even sleep in my bed with my hubby wen master 5 is here; well he turned around and told hubby he doesnt want a sibling because its mine not his mothers & ever since has taken to punching me in the stomach wen he has the chance. Wat concerns me more is tonight said 5yr old attempted to stab my 7yr old son not once but twice and was caught by his aunt, he refused to apologize as he didnt see how he was in the wrong and put the tears on wen my SIL went and got hubby, master 5 then rung his mother crying saying that his aunt & i were being mean. He then asked his mother y his dad doesnt sleep over at their house anymore to which his mother replied because he married me to which master 5 just said well cant we get rid of her?! Im seriously starting to think this child is the devil, my 7yr old is sleeping with me tonight as i dont feel comfortable having him sleep in the bunks with master 5. But im lost and gobsmacked at the extent this child is going to to rid his father of myself & our kids. I feel our newborn wont be safe wen he/she arrives if this is how master 5 is carrying on now