Hugs and deep calming breaths
. Give yourself a break hun, she's 8 weeks and you have two other LOs to deal with. It is FINE to not have a perfect routine, in fact most mums of three will tell you number three just has to fit in. I know that's tiring and it's so hard to switch off the EASY mindset, but I do think if you can accept that things will be messy that will kind of take the pressure off a bit if you see what I mean?
I only have two LOs but what I did with DS was set small goals and try to feel positive if we managed those. So at this stage all I tried to do was aim for roughly 3h feeds, and a rough EAS pattern. Tried for a sleep when he seemed tired. I tried one nap a day half-heartedly in the crib - by that I mean if he hadn't settled in 10-15 mins max I gave up and just put him in the sling. I also made a deliberate choice not to try to resettle naps - very liberating
I remember 8 weeks being particularly rough though - tends to be the peak of crying, it's a WW and often a growth spurt too. So, if you can, make the choice to do some 'deliberate parenting', get the sleep in when and however you can, try to learn cues but accept it won't work out right every time. We had a set BT too which helped, he would usually settle well then even if the day was all over the place
As for what to tell your mum - I would just give her a rough idea of when feeds are due and let her handle the sleep. Often grandparents are great for this - much as they frustrate us sometimes by keeping LOs up way too long they also tend not to stress so much about how long naps happen to be and will just cuddle, rock, walk or whatever is needed to get through the day. Something we can learn from I think
Keep going, the early days are hard but they will pass. Here to support xx