Pregnancy and New Job

So I just found out I was pregnant (planned but happened a lot faster than I thought it would) I’ve been at my company for 6 months and I know they are legally not able to ask me if I’m pregnant and I only have to give them a months notice beforehand but I really don’t want to do that. They hired me even though I was highly unqualified for my position (not anymore). I’m just scared I won’t have a job to return to after maternity leave. I run a whole division and me leaving would be a huge impact. I want to discuss my options with HR before I actually tell my boss. Also I want to take 6 ( they do offer up to 12 weeks unpaid but need the money) weeks just getting used to having 3 kids but since I do run this division I was thinking that up until a spot opens at the daycare my other kids go to that I would bring baby along with me. 1. Is it possible for them to replace me while I am on maternity leave? 2) how long should I wait to say something 3) should I consult HR first 4) do you think it’s possible they would allow me to bring the baby to work for a few weeks until my spot in the daycare opens up in September? All advise appreciated