Can hardly believe this is whats happening?? Is she mating only with Pip or do we even know? This is not normal is it?
Ella and Hart have been spring/fall buddies for years so that part isn't unusual. Hart is a little more gung-ho in his courting than other birds (freaking little Engergizer Bunny actually) and he and Ella were happily setting up shop at the Radisson before Pip arrived. What is different is that he's now at her old nestsite (remember she can see the whole city from the roof of the Radisson) and none of the ladies he's been courting as settled down with him, if they had, they would be defending the site and Ella would be consolidating her residency at the Radisson.
I don't know why Hart's ladies aren't staying around, but I suspect it's because Ella keeps turning up - or maybe the ladies are working it out among themselves. End result is that there is not female to keep Ella from visiting her old nestsite and since Hart is offering food to ladies (any ladies obviously) - she's taking him up on his offer. And because she's sort at the peak of her cycle, copulation is also not a surprise, but at this point likely not contributing to the egg count midway through laying. Better to think of it as an hormonal reflex - both with Hart and Pip.
As for who this year's daddy is? Well I'd need to check Pip's return date. Usually that gives us a good idea of who is most like the dad. Copulation takes place over a long time, some research even says it can/does start while on migration with whomever - peregrine foreplay if you like. Copulation changes in frequency and duration as the cycle continues and many of the copulations are just going through the motions. There has been research on paternity but I don't remember what they found was the rate of offspring from extracurricular copulations but will see if I can find it again. It may also be that male peregrines aren't so concerned that all their offspring are theirs rather having a nestsite increases their likelihood of attracting a mate and that increases their chances of passing on their genes ... same with defending said territory, providing food, courting enthusiastically, copulating when the female offers, being attentive to helping with incubation/child-rearing, etc. By doing all that, his chances of a) having offspring increases exponentially and b) for any offspring he does father it improves their chance of survival. A peregrine's genetic success is if his offspring have offspring - Pip needs to do a good job with his chicks through to September so they have their best chance to survive until they in turn find a mate and a nestsite and they have young. Genetics is the long game peregrines may or may not know they are playing.