Tiktokt hasnt posted yet or I'd say just listen to her.
First thing is you need to make sure little Molly is feeding well, this can be told by her nappies, how long/often she feeds for/if she seems satisfied after a feed etc, weight is only an indicator, it is not the be all and end all!
FGS Alex went from 10lb 3oz to 8lb 15oz in four days! The only reason we werent referred t paeds was because I knew the rest of it and said I wasnt happy with that weight being the issue when I knew he was feeding well, but you need to be sure of this, from your OP you do seem sure, but I'd call a Bf helpline just to get someone physical on the otehr end of the phone agreeing with you, k?
Remember these people told you it's not feasible to feed with flat nipples!!!
As for having to use formula, tell them to fuck off, no-one can make you use it, if she is having an issue with her weight best thing is for you to feed her as much as you possibly can, I second what someone said about the babymoon, turn your phones off, get DSD a few DVDs and some snakcs for the both fo you and the then go to bed (Is DP off work still? If not DSD is old enough to help out anyway, she could always get into bed with you!) skin-to-skin as much as possible and keep M practically latched on constantly, even three or four sucks (Which seems liek sod all to us) is doing something y'know?
Obviously be aware that losing weight is not good, if she is happy to take the boob though, I don;t see how you fafing about expressing is going to help her, yeah sure, taker her off the breast to exoress so you can give her more nah. Put her to the breast more.
Lastly, you're not a failure, if you decide to FF then that's ok honey, it's fine, but make sure it's a dcision you make and not one youre forced into. Stand your ground, tell them you know what you're talking about and hopefully they'll get you some proper help, do they have BF clinics etc in Jersey???
I'm sure someone will know.
Love to you & M, remember J and DP need to help, give J the 'big sister jobs' and as for DP, I'm sure he'll do as he;s told.
(Was J BF? I'm sure it won't help your feelings eitehr way, but remember, different situation, totally different, you;re a great mum.)