I think the social media stuff is all SaW and the initial use of BW's phone could only be SaW. It was topped up with credit bought using SaW's card (could ScW have borrowed SaW's purse to go and get some milk on the 18th at 6.16pm returning after 6.54pm?). That may all be presented by the defence as about the abuse allegations (Devil's Advocate again). After that, I'm certain that the phones are travelling together but it is not impossible for ScW to be the only one with the phones. As yet there are no sightings or CCTV of them together at these times. I am pretty certain ScW murdered BW and buried her in the early hours of 19th.
I have a feeling SaW will be aquitted of the two remaining charges and will be sentenced to the period of time on remand for the two she's pleaded guilty to, and to walk from the court. I expect ScW will never see the light of day again.