Not sure I totally agree with this - I don't think Ioan can get, nor would want 100% custody. He is in a difficult place in that he is a B-/C+ list actor and right now has to take what work is given and invariably this means working away from home for large chunks. He also made a key mistake, in my opinion, in going to Australia and missing 2 key therapy sessions - I question whether that was essential. That, together with his extended holiday in the UK is likely to have given the girls the firm impression that they come second after Bianca. This, with the other missing session (work in NY) plus Alice's shenanigans mean the therapy has not happened meaningfully for the girls at a critical time. I think Ioan is in a truly awful position but I also think he has made mistakes.
The likelihood of him getting 100% custody is moot anyway. No-one can prove - to the burden of proof required for the courts/CPS - that Alice is abusive or neglectful to her children. Her PA is clear but again that has gone on so long now and is so entrenched that it may work against Ioan getting any custody at all (in particular for Ella as she may refuse to engage and the courts won't force her). If regular therapy isn't immediately instituted (and it's doubtful it will for months and months due to the slow pace of the court) it's unlikely anything will change. And if therapy doesn't work, the only thing to hope is that Alice will do a Betty Broderick and drop the kids off with him to try and break up him and B.
It is a horrible crappy situation, but sadly it's one that happens on an all-too regular basis in divorce cases. Unfortunately it is usually the father who is alienated. Alice, the evil bleep, will likely succeed with her PA in the short term, but long term, once they are adult, I am sure they will start to see the truth and will re-develop a relationship with Ioan.