I post here with trepidation as a step mother - but want to know how others handle this and maybe just need to vent.
I have (I think fairly successfully) brought up 3 teenagers alone now ranging from 20-15 and my job involves being with a lot of teenagers.
Have been with OH since DSDs were 3 and 5 they are now 10 and 12. I love them dearly and their dad is away a lot and I have them when he isn't around (to give context). We live in a different town 250 miles away.
Did have v good relationship with their mum until recently where I expressed concerns over the girls safety and she no longer speaks to me. The girls are aware of this (their mother told them) and it has caused tension and I feel they are more guarded with me.
We have them for half the holidays so they are here now.
When they are here it's often the only time I see OH too so will often do things the four of us. We try to do things which involve spending time rather than money. DSD1 who is 12 often likes to cook with me (I try to persuade OH to do it too to have 1 on 1 time with her) and up until now I have a good relationship with her.
This time however I think maybe hormones have hit and she isn't interested in doing anything other than being on phone/tablet and is really moody and stroppy and resentful when we take her out somewhere - only interest she shows is when she might get bought something 
I am handling this by asking her not to speak to me like that (constant back chatting and questioning everything she is asked to do) and walking away and letting OH deal with it where possible.
Yesterday we took them for a bike ride (DSD2 really wanted to go on one) and she refused to ride and sat on a bench sulking. We spent more time putting the bikes on the car than actually riding. I lost it with her and raised my voice and told her her attitude was doing my head in and I had had enough and she cried - and I felt terrible and like a absolute bitch.
Thing is I know how to deal with my own teenagers but this is really tricky, I had really steadfast rules but OH tends to bend the rules a lot with DSDS and I am trying to stick to the agreed rules but he is them backing down and I feel hanging me out to dry a bit (I.E.: pandering to her strops, saying no film later then backing down, allowing them to chuck half their dinner in the bin then half an hour later letting them raid the fridge for fruit).
I don't really know where I am at and how "involved" I am supposed to get now they are a bit older. I guess also if I am honest I am on leave, all my kids are away and I really want to relax a bit and maybe feel a teeny bit resentful however important I feel it is for OH/us to be involved. I sometimes want to go and meet my friends (for lunch etc) and leave them to it but OH really wants me to spend time with them.
How do people handle teenage step kids being directly rude to you - this is only going to get worse - ATM I try to turn things into a joke to defuse the situation.