Fast forward to the early 2000's and you can now see the continuity headache beginning to manifest. If Peggy and Sharon are siblings....how could one have been active during WWII, some 70-odd years ago, while the other appears to be active and youthful in the present day? I mean, how old must their parents have been?!
Speaking of Peggy and Sharon's parents, we are introduced to Amanda and Harrison Carter in Captain America (vol. 1) #162 wherein we learn the familial connection between Cap's two love interests. I have not been able to find a definitive issue that identifies Peggy and Sharon's parents as Amanda and Harrison but as near as I can tell, it's likely a new piece of information introduced in a Marvel Handbook entry.
In recent years, Captain America writer Ed Brubaker introduced a retcon to alleviate the knots of continuity by instead making Peggy Carter Sharon's Aunt. I have to admit this does go some way toward helping the problem, but I wonder how future generations will fix this? Great Aunt? Great-great Aunt? Some dialog in Captain America (vol. 5) #49 suggest that Brubaker's intention was to make Sharon's father (Harrison Carter) Peggy's brother and that Sharon was a 'late surprise' for her parents.
Of course, any retcons introduced after the MC2 began aren't considered canonical unless otherwise mentioned and so, for the purposes of this Family Tree....Sharon and Peggy would still be- somehow- siblings! In fact, it's even expressly stated during flashbacks to Shannon Carter's origins in both Spider-Girl #32 and American Dream #2.
Despite being referred to colloquially as 'Aunt Peggy', Peggy herself clarifies that she is a cousin of Shannon's father. As for Shannon's parents, they have not been given names, neither on-panel nor in any Handbook entries. The little that we do know of Shannon's parents comes from a single panel in American Dream #1. Shannon's mother was a second grade teacher and Shannon's father was a police officer in their small Midwestern hometown.
While it's really hard to reconcile a WWII veteran like Peggy being seen in the same panels as future generation hero American Dream without suggesting Infinity Formula's or the like, I do have a possible No-Prize explanation. Simply put: the MC2's Peggy Carter is not WWII veteran. I know it seems silly, but notice that no mention is ever made to her knowing Captain America during the second World War. Mention is made only of her time working with the Avengers on-staff, events which chronologically would take place roughly 20-30 years prior to the present of the MC2. Considering that Peggy is of an advanced age, but not an impossibly old age I think it can be argued that this particular point of continuity is different in the MC2.
Something else that jumped out at me is the fact that it was Peggy who was the next of kin to Shannon, rather than Sharon. In fact, Sharon is only ever referred to in the past-tense, leaving me to wonder if perhaps....Sharon remained 'dead' in the MC2. You see, back in Captain America #237, Sharon apparently died. It wasn't until the Mark Waid penned Captain America #445 that readers learned that she had not actually perished. Considering the later story came out shortly before the Marvel Universe suffered a dramatic shake up and the wibbly nature of this period of time in relation to the MC2's own history and point of divergence, an argument could be made either way.
*UPDATE* Upon further investigation, it would appear that Sharon Carter did, in fact, die at some point in the past. Or at the very least Captain America believes her dead and she hasn't resurfaced in the 10 or more years since his absence. From A-Next #10:
Until I find a more convoluted and pointless reason to scrub through half-century-old comics, I remain
frogoat