If he had said he killed them at home that would have spawned even more of the exMRS type of SW bashing (even NOW they are still at it, permitting vile new comments that will remain. what, forever?) . (He flew off the handle in rage, that horrid woman 1) questioned his manhood 2) said he couldn't have the kids 50% of the time 3) called him a liar, a cheat, 4) she fed him chemicals thru patches, 5) whatever, it was her fault she got herself killed, because, well, FB videos.
I think if he killed them at home there would have been a lot of dog evidence, we just didn't see enough evidence.
Taking them to Cervi took very little extra time, if any, and spread the evidence out to hide the trail. Except for burying her the way he did, oops. (Another reason I don't really buy long-planned pre-meditation, it would not have been hard for him to dig an adequate grave earlier, cover it up with brush, at least make it softer to dig in).
I think he was completely honest when he told Coder and Lee that only "minutes" elapsed from killing SW to getting her to the truck. Note at that time they weren't asking him about the kids.