My DP has 4 children with his ex. (I have just 2 of my own).
They have always had a basic routine that he/we have the DCs every weekend and their mum has them in the week. Generally speaking they all come together, and I'd agree with what foolonthehill says that does reinforce the bonds they have between them to be together most of the time. It also fits in better with working routines, etc and my DP very much switches into family mode at weekends and work mode in the week.
There are downsides to this arrangement though - when I first met him my DP did struggle to look after 4 at once on his own, and a lot of responsibility ended up falling on his eldest (12 at the time they split, 16 now), both to help out with the younger kids and to support DP at times when he was ill or anything. The younger ones are also quite competative over getting any parental attention - I think it's quite hard to be a single parent to 4 at once all wanting a piece of you.
My DP's ex ocassionally takes just one child off for some one to one time at the weekend. I've always encouraged my DP to do likewise but he's reluctant to forgo time with the others, and doesn't have any spare time in the week. It's something I think would benefit the DCs for both him and his ex to do more of.
Me and my ex agree a couple of weekends a year when we take one DC each, and spend it doing something they particuarly enjoy. I've had some wonderful walking trips with DS and theatre trips with DD, which we've really enjoyed. Would definitely recommend trying to structure in a bit of one to one time, for each child at least a couple of times a year.
You're obviosly right in the throws of splitting up at the moment - it does get better. All our DCs seem find about their living arrangements, completely used to having their parents in different houses. It just becomes normal and life goes on. Good luck.