Re: gMail email separation
Very difficult to identify most recent responses in email chains if multiple responses come in.
They should be in the order in which they were sent, according to your local time (IOW, if someone in California sent an email at noon
his local time and someone in NY sent an email at 2:59 PM
his local time, the one from NY should show as being sent earlier). Two sent at exactly the same second may be in either order.
As far as not grouping the emails from one sender together, that's different for different clients, it has nothing to do with the account. I don't think the GMail app can do that, but it's been a long time since I uninstalled it. I could probably write a worse email app if I really tried, but almost anything out there is better. (I know Thunderbird - for which there's no Android version. But I think K9 can be set the way you want (and it has a lot of other nice features - even PGP if you want some privacy).