I have 2 lovely stepkids (age 8 and 10) who I've known since they were tiny. Their mum left DP for another man when youngest was a baby.
DP and I moved in together 6months ago and we have the kids every other weekend. We're getting married this June.
Stepkids' mum re-married years ago and lives 20 mins drive away. She has social anxiety and avoids me whenever possible, communicating mainly via DP. Since I've been living with DP she's become increasingly fussy about everything I do with the kids... from what I feed them to how I dress them, even telling DP I must not tell them ghost stories (when they ask me to) because she is religious! She is also very odd about their clothes... despite recieving £800 per month child-maintenance from DP she always asks for more, saying things like she can't afford new school shoes! DP thinks this is reasonable and says kids are 'expensive'. He also pays half of all school trips (usually 2 each per year including ski trips) and goes half with her on their birthday presents in addition to getting presents from us. She's a sahp by choice and her new husband's a waiter so doesn't earn much.
She refuses to provide clothes for kids to wear on weekends they spend with us. She insists I make them change out of 'her' clothes as soon as they arrive and must put on 'her' clothes again before they leave. I have to return 'her' underwear in a bag which is not always easy as kids tend to take socks off around house or leave pants down side of bed. Today when she dropped them off she crossly told me she was missing one of DD's socks and a pair of knickers from 2 weeks ago!! As if this is very very important.
She is also scathing about the clothes I buy for her kids. She buys expensive brands, I buy Next and for playing in garden I get Primark as it tends to get ruined by grass-stains, mud etc. She saw a photo of DD wearing a pink tracksuit (DD's choice) and told DP it looks tacky and I'm not to dress her in pink!

What's going on? AIBU or is she?