I think maybe you're just stressed and overwhelmed?Having and taking care of a newborn/infant is difficult,and taking care of a 2 yr old is also difficult,so both together can cause stress and being overwhelmed,which results in anger,not being patient,being easily irritated,etc.You're not a bad mom,maybe you just don't know how to juggle things,or sores your duties and time evenly,or you forget to sit back and relax and keep your cool.Many reasons.Try to take some time to think what is really bothering you,what's the source?Is it actually the children,or is it being overwhelmed with motherly duties?Is it your mother and the sadness?Is there anyone to help you out physically?and anyone there for you emotionally? Try to remember that they're you're lovely children,just beginners and don't mean to make you upset.Always tell yourself to be understanding of them,try reading up on their development which would give you a better sense of why they may act a certain way and do certain things and how they are progressing individually and what their temperaments are.Try to tell yourself to be calm,talk calmy,be slow to speak,and be patient.For me,prayer really helps no matter the situation,you can do that too.Dont lose confidence either,I'm sure you're a great mom who is doing her best,and you can overcome this obstacle!Even though it seems hard,you can do it=)