I am sorry if I am posting this in the wrong place. I just don't know where is best and I suppose I could do with some opinions.
I have 2 dc from my 1st marriage - ds nearly 11 and dd 8. They go to their dad's every other weekend (ish - we are very flexible) and every wednesday night. We split when ds was 3 and dd 6 months, so a long time ago and dd has never known it any different. He left me (he actually told me he was going to leave when I was 7 months pregnant) for her - now his wife. I am also now remarried with dt's.
Despite everything, me and ex dh are very good friends. There is NO animosity between us, we are flexible with visits, I have absolutely no interest in being bitter and angry, I will do my utmost to make sure my kids know they are truly loved by us both, and he feels the same. They adore him and love spending time with him.
However, on numerous occasions I hear really bad stuff from them about their stepmum. She has always been quite strict with them (fair enough) but I am sure some things are just not normal?
For eg, she tells them what to wear every day they are there. She will lay out their clothes for them. This weekend just gone she went away on sat morning and actually told dd what to wear on sunday. They are not allowed to wear their clothes from home and sometimes have to get changed back into their school uniform in the car on sunday evening when returning home (if they went there straight from school). In 7.5 years I have only ever seen about 2/3 outfits of theirs from that house.
She will gently tell them to go upstairs to get out of their PJ's and then follow them 2 mins later in order to tell them off about something, out of daddy's earshot.
They have been made to be extremely fearful of going to the loo in the night - dd tells me she tiptoes into the bathroom, puts the toilet seat leaning on her back so as not to make a noise and 'stop starts' her wee in order not to wake her up.
A fun thing that ex dh does with them occasionally is let them chose what they want to eat one meal - literally anything, sweets, crisps, whatever! It is a fun thing they do maybe twice a year but on sat morning at the airport she took them to one side and told them it wasn't fair on daddy to have to make 3 meals so make sure they only choose one. Deflated children who instantly loose the feeling of fun. 
I could go on really. And like ds said last night 'it is lots of really small, some medium things that happen but when you add them all up it's really big'. And then between sobs he said into his pillow 'I wish she would just go away, I wish she would just stay in New York'.
dd said she wishes that in the first place we had never split up (obviously) but the second best situation would be that he had married someone 'kind'.
Last night she was literally wailing about her, bought on I think by the fact that they have had a really fun and lovely weekend with just daddy.
Please, what can I do? I feel so sad for them that they are so torn. They obviously want to see daddy but just wish she wasn't there. I hasten to add that I have spoken about it to ex dh about it only a couple of times because I really don't want to seem a bitter iyswim. And that conversation only came about because dd had refused to go to his for the first time one weekend because she claimed that stepmum had hit her for turning on her bedside light so she could retrieve a toy.
I can talk to him again, but apart from leaving her, which of course is ridiculous, what can he do? Alot of stuff is said to them without him even knowing.
Sorry it's so long, I just feel like a lioness in need of protecting her cubs, but really don't know how