I don't think the names mentioned by you will substantially improve us, some of them may be an upgrade but not by a lot.
I think that Smalling is probably the only one I would be happy with as I think he is a good defender and at a good age.
I think Williams, Schneiderlin, Mirallas and Besic will leave this summer. Martina will probably stay as cover in case of injuries or suspensions and is probably not hugely expensive.
I think Jagielka may leave as he probably won't want to spend possibly his last premiership season just sitting on a bench. However, I would be glad to keep him as an experienced back up centre half .
Robles is out of contract and I think Niasse will leave as well .
Sandro , if he can find a club .
That is probably anything up to ten players from the first team squad off the payroll and I think we will see a lot of the under 23s go as well...Williams, Galloway, Browning, Pennington, Connolly to name just five.