I was raised Catholic and (as per a previous rambly post) have recently been exploring different denominations and how they differ to Catholisism. There are a few Ecumenical churches near us. One in particular is a group of churches and lists Methodist, Baptist, CofE and United Reformed.
I'm curious but confused about them! Do they just have one Sunday service or different ones for each denomination? If you are baptised there, what 'are' you?
I can't answer about the services - you'd probably do better looking at their noticeboard or website.
But as to baptism, you are only baptised as a Christian, not into any particular denomination, so it doesn't really matter. I know to an RC that's probably an odd idea, as being an RC or not is a big issue. But in Protestant denominations it's becoming a member as an adult which makes you one denomination or another, and they all respect each other's baptisms. I'm pretty sure the RC are also happy to accept baptism in any mainstream protestant denomination (ie ones which believe in the Trinity)
I can't answer your question about how this specific grouping does things - I'd guess they basically all muck in together. But having been raised in a family which included members of all the denominations you list, they really are similar enough to co-exist, and are certainly happy to take communion with each other (though you may find the nonconformists insist on non-alcoholic wine! )