I would introduce Riz Lateef as a news presenter
If you have the tens of thousands of pounds to spend, then go ahead.
If sian decides not to move then I would give Bill a new partner maybe Kate Silverton.
In what way would Kate be a "new" presenter?
Do you not think Chris Hollins might get bored at some point in the future and want to move on? He could easily be poached by a competitor or quit to do something else, now he's done 'Strictly'.
Make Matt Taylor the main weekday weather presenter
What makes you think Carol would just go to weekends - a serious demotion? You really don't understand how this stuff works, do you? I very much doubt Carol would just move to weekends - and I'm sure you'll find her contract states when she works, meaning her employer couldn't just change the terms of their agreement like that. Presenters seem more often than not seem to quit - or at least threaten to quit - before taking a public demotion (Penny Smith would be a good example, being told she'd lose the newshour and only get to present news updates).
If you move Carol off Breakfast (why I'm not sure) you'd need to move her to the same position Louise Lear and Helen Willetts have - appearing on the NC, six, ten and weekend bulletins.
and move carol to weekends also bring breakfast from the breakfast studio of a weekend rather than bbc news channel studio.
Again, if you want to pay the huge costs for that, go ahead. I'd rather they saved the money, myself. It is necessary for the weekday version to come from a different studio to allow the NC to break away - at 08:30 or during breaking news/ conferences. There isn't this need at weekends.