2 kids to 3 kids

How easy is it to adjust from two kids to three kids because I’m struggling so badly my little one is 3 weeks old and she is going through it to where she only wants to be held to sleep and my 4 year old gets night terrors and both were crying and I couldn’t understand my four year old so I started crying and then he finally said that he just needs me and his baby sister was crying and so I just held them both and rocked them and cried silently and my husband is sleeping in our 5 year olds room because she’s been feeling super left out and I just feel like I’m failing as a mom I’m not depressed or having any thoughts like that I just feel like I could do better as a mom and I’m trying my hardest everyone that said they would help out and come and see baby never did and my mil keeps trying to baby my husband because she keeps asking him for over $3000 and keeps saying she will pay us back and so I’m also dealing with that which my husband told her no but she keeps asking no matter what we tell her it’s just a lot to adjust to especially since we need to start school shopping and then I have to get my new born on the school schedule as well as my two littles that have never gone to school yet I’m just so stressed