Sleep deprived mom

Can someone help with tips to be a calmer parent? I’m normally calm about things and don’t get stressed easy but the past 2 weeks my 3 year old has been waking up between 4 and 5 either to watch the iPad (he doesn’t take it to bed) to play with the cat or just because he can. If I say no to any of these he screams the house down, I don’t give in to any of those because he doesn’t go back to sleep if I do and either way he doesn’t anyway. I have a nearly 3 month old that wakes up every few hours as I’m breastfeeding but that isn’t a problem as I’m used to that and we normally go back off to sleep. Since my toddlers been waking up and screaming he wakes the baby up and the baby doesn’t end up going back to sleep either. I’m really irritable and tired I feel mentally and physically exhausted and I’m getting to my wits end, he is pushing my buttons and the best of it he thinks it’s funny or just hits me with a “not my fault”. I don’t like shouting at him but the past week it’s all I’ve been doing because he isn’t listening doing the opposite and obviously I’m exhausted. Sometimes I feel it’s easier to give up but obviously I’m not going to as I love my children. I also feel like my milk supply is decreasing due to lack of sleep and stress. Help please!!

I’m 24 n my first sons father isn’t involved due to past domestic abuse n currently being in jail & the baby’s father lives at a different address and is always at work.