I agree with (most of!) Mummy_AllyK, it really is much better for the kids.
I do personally think kids should spend more time with their fathers though because Dad's are integral to a child's development. I believe that every second weekend isn't enough time and it doesn't give the child the experience of both parents being involved in school etc. There is the occasion where some Dads don't want that extra time so there is no point pushing it.
The 70% stat I can't imagine to be true, especially for non extreme circumstances (no accusations of assault, violence, etc.) if both parents are good parents the court looks to 'substantial and significant time' with the non custodial parent.
The way that your two replies have some agreements and some disagreements just goes to show how sensitive and unique each situation of child arrangement after separation is!
Which leads me to say...
If you feel that 50/50 will work for your kids (it definitely can work when parents get along from the start!) well go with that and try to make their place they stay with you as comfortable as possible. Getting a place just for you and the kids is a priority. Accept their behavioural changes and continue to love and nurture and raise them with your ex. Continue to communicate with your ex about how the kids are when they are with him, etc.