First, a tip in good conduct: not everyone is going to say what you want to hear. Learn to deal with it graciously, because if you speak to the judge with a tone that indicates the use of four exclamation points, it's going to hurt your credibility and your case. Further, it's important to learn how to take things with a grain of salt, instead of jumping straight on the defensive, because the judges in parenting matters are quite often as harsh as they are unforgiving, and I've never found them to be particularly tolerant of petulance.
So, mediation failed because you and your ex couldn't reach agreement. For most parents in this situation, the next step is to file an initiating application with the Court for parenting orders.
Whether you, he, or neither files an initiating application, negotiation can continue outside of mediation (and this is most likely what your lawyers will be referring to when they say they'll 'hash it out' - they mean they'll continue negotiating with the goal of getting you and your ex to agreement). Only 5% of cases initiated actually result in orders made following trial; the other 95% settle by consent either before, or on the day of trial.
There are lots and lots posts on this forum about the Court process, what the Court takes into consideration when determining parenting orders, etc, so I strongly suggest having a read through some of the older threads. I think I've maybe discussed it from time to time on your other threads, as well, so rather than talk about that, I will talk instead about your desire to include the children in the decision at hand.
From memory, you have five kids, one quite a bit younger than the other four, and one now an adult, so no longer subject to parenting orders. I would hope I wouldn't need to state the obvious here, but the youngest isn't in a position to determine what's in her own best interests, so she should excluded from the decision entirely.
The older three who can be affected by parenting orders, however, can have their voices heard in a couple of different ways.
One is that you can try mediation again, but this time seek out a child-inclusive family dispute resolution conference. In these circumstances, the kids will speak to a child specialist about their wishes, and that will then be communicated to you and their father ahead of a mediation session, so that you can take their views, as communicated to an objective third party (which is usually with whom they are most honest) into consideration when discussing a possible care arrangement.
Alternatively, if this proceeds to Court, the Court will most likely order the parties to undertake a family report, which is where a specialist interviews and observes the parents and the children to ascertain their views about what they want from the care arrangements. This is then communicated to the Court (and to the parties) in a report, along with the specialist's assessment of the situation, and their recommendations. This is the only real method the Court will accept as a way to learn what the kids' wishes are, as a consideration of children's best interests under s 60CC of the Family Law Act, because it is the most unbiased method.
Try and remember that your ex's position is just as valid as your own, and there is every likelihood in the world that the kids have, indeed, told him that they want to live with him, just as they may have told you the same thing. It's unwise, therefore, to argue that you know the kids' "real" feelings and that your ex doesn't, because is probably arguing the same thing.
