Check-in on DL ticket with KL first leg
 

I am hoping the experts can give me some advice. I did a search of the forum and was suprised I could not find the answers. In a couple of weeks Mrs. CEUflyer and I are flying CPH-AMS-ATL-YYY, where YYY are different cities in the US (so we are on separate PNRs). CPH-AMS is on KL, the rest is DL. They are DL tickets.
I know that KL opens intra-europe seat selection and check-in at T-30 hours. Here are my questions:

1) Where do we check-in online? delta.com or klm.com?
2) When can we check-in online? T-30 or T-24 from the first flight on Delta metal (AMS-ATL). I'd like to have a good shot at adjacent seats CPH-AMS.
3) Are there any pitfalls or problems we are likely to encounter?

We only have 1.5 hours in AMS so, I'd really like to avoid having to get onward BPs there. I do have the KLM record locators. KLM shows all of my flights correctly, but for Mrs. CEUflyer, it only lists the lone KLM flight (though the ticket on dl.com looks fine). I guessing this could complicate things.

Thanks in advance for your help!

You must check in with KLM if that is your first leg. DL.com will automatically re-direct you.

avidflyer pretty much answered everything but just to be clear:

1) klm.com with your e-ticket number (006....) delta.com will send you there if you try to do it from "my trips".
2) T-30 on klm.com. T-24 on delta.com (the check-in button wont show up). so just go directly to klm.com
3) just open 2 browsers and make you sure you get seats next to each other on the first segment. you need to fill in your passport info.

Thanks for the replies. Just to confirm, if I check-in at T-30 on klm.com, will I get onward BPs for the DL segments?

Yes. It prints all on one page if I remember correctly.