vq - 'extended parenting group' sounds so good if, as you say, all work as a team for the children's security. Sadly this is not always the case. Sadly too, as in my experience, it is often the mother who uses the children to punish the father and of course the children suffer. I have to be fair and say I know of one father who has also alienated his children from their mother.
I have tried to stay neutral for my DGC and maintained their stability as much as I can. They stay with their father and myself at weekends and more in school holidays and appear to be settled into this routine. However there have been upsets and disruptions along the way due to Mum's demands. She can be quite adamant about 'my time' and 'your time' which causes problems when some flexibility is required eg football training, school clubs, swimming lessons etc. On the other hand if she wants to go out we are expected to look after them in 'her time' (eg a week's holiday this summer)! Frankly it's not worth the arguments.
The children are all under 8, the youngest being 3 and we have suffered night terrors, sleep walking, bad (violent) behaviour and soiling pants (in the case of the youngest). Yes children are adaptable but they do pick up on conflict. So william09 all I can advise is to try not to get involved in any disputes and hang on in there as the stable one whatever else happens.