I think have to make a routine for them? And since #1 is the eldest, he or she might feel left out and unloved due to the arrival of #2. They need more attention but not getting much of it that’s why always throwing tantrums. Also, toddler age is where they learn how to do this and that, so it is best to keep reassuring and be calm around your toddler. My 17 month old is also starting to annoy the crap out of me at times and I’m 21 weeks pregnant with #2. I don’t know how it will be like when #2 is born. I’m planning to have a routine for both of them and educate my firstborn to sayang, be patient and self-soothe when she doesn’t get her way. I know it will be hell when one wants to sleep but the other is whining and crying, so I think best is to separate them for a timeout especially the elder one, settle the younger one first then adopt gentle parenting on the firstborn. We have to make them understand they are big brothers or sisters and they have a big responsibility to play. Make sure to make time for them too, talk about how they were also babies last time and how much they needed us too. Tell them to watch and learn too, make it an enjoyable routine along the way.
I’m just saying out loud, really don’t know what to expect when I give birth to my #2, hahaha. But all the best and good luck, can try watching videos on gentle parenting?