So I brought this subject up at counselling, and we talked at length about the pocket money situation.
Counsellor wants us to sit down and work out a compromise for all. He wants us to include the kids in the process and decision making.
We talked a lot about boundaries and dp being less "airy fairy" with his kids. All sounds good in theory.
However, I have told dp and the counsellor that I don't trust dp to go through with the boundary process and counsellor said that this is a good place to start as its less confrontational than some other issues. If one of us lets the process down, then we can discuss it.
However, in the car on the way home, I again said to dp, "what happens if dsd runs out of money and then gets opportunity to go somewhere nice but doesn't have enough money to go". His words were "well, I'd have all the best intentions to stick to things" and that he wants to "try" to do this. He said he couldn't make any promises.
I feel physically sick at the thought of sitting down with dp, ds and dsc and allowing them to all decide some extravagant figure whilst I get to be bad cop, hopefully get some compromise only to have dp undermine me and give dsc more money behind my back.
There are some other issues regarding money and dsc and dp fiddling things to ensure they get more than they are entitled to. Nothing illegal, just immoral, in my opinion. I can't go into details.
What also came up is that maybe I have some control issues over my ds. Ie. I don't want to relinquish control over ds to hand to dp. So I know that anything I say about not wanting to discuss pocket money with kids is going to be said that its because I'm scared of letting go. But I really feel now that I don't want to have this discussion with the kids, it will be a farce as far as I'm concerned, and teach the dsc that I am not to be respected or listened to because ultimately dp is in charge when/if he gives them extra. Whilst I will be sticking to the rules.
Truth is I don't trust my dp to parent ANY of the children properly and be fair to them.
The first thing he said when we got out of counselling was that he was glad I didn't get all my own way and I asked him if he was glad that I got a "telling off" and he admitted he was glad and that he's always said that it's "my way" or no way. 
Counsellor has said that by having two sets of rules in house, it just makes the other parent cling on even more to "their" rules as it feels like a loss of control to give in. I really think this is what I am feeling and I feel damned if I should give in on this because we're not playing the same game.