There is no clear line that McDaniels and JRob are close. I've said this before but...JRob was a traveling scout the first time McDaniels was there. As you know, he was in Tampa after getting promoted in NE. They spent about a year together.
Schwartz and JRob are super close. Their families do holidays together and wives are friends and some have even said their houses are near each other. Schwartz not only also worked for New England and grew up under BB, (and the career stuff most know) but he worked for the NFL out of the Titans building before he took the Eagles job. He was JRob's choice and interviewed, but Amy wanted continuity and bought into Mularkey's plan. Amy also heard too many good things of Lebeau and it was widely assumed hiring Schwartz would remove Lebeau, 4-3 3-4 switching.
McDaniels (which I don't agree with....can't give credit for coaching a legend when there's identical success without him) seems to be the top offensive candidate while Schwartz (doing well with limited roster, two years now) is the top defensive candidate. JRob would probably consider either just like any GM. I'm NOT saying he'd never hire McDaniels. There's pedigree and success, just that I've been told over n over that they are not the close NE people others make them out to be.
As I mentioned, Lebeau seemed to let Spanos call the 4th Q and that was hmmm. With the Titans, Lebeau has run a 5-3 more than any other set but no one wants to call it that. 3-5 with two LBs on the line...call it what ya want. His time with the Titans has not at all been all 3-4 as his prior career suggests. He's adapted and it is not at all clear whether Lebeau will stay with the new coach. He's super well respected and highly regarded. It will (almost) be entirely up to him.
Spanos has long been considered the heir. He is a former DC that coached several names at UCLA. What I love about him is that he wants guys to know many positions. Aaron Wallace had such a bad luck injury this year. He got a veteran's day off and worked out on his tweaked back, that wound up being too painful and he surprisingly sat the year. He was expected to be a big contributor in 17. He not only has played all four LB positions in the NFL but he was playing that spy safety near the LOS (polamalu to some degree, against the run) role in preseason. Jayon Brown played all four LB spots this year. Nate Palmer, a former GB starter and almost exclusively ST in Ten, learned all four spots and played them in preseason. He also believed that depth defensive backs should know both safety and cornerback. During the preseason it was fun to watch the DBs switch between plays. I think it's outstanding for flexibility, communication, and understanding how the defense works. It should but it hasn't shown any gains as far as depth just yet.
Schwartz would likely appreciate both Spanos and Lebeau.
Russ Grimm is a HOFer that is so well known. It's hard to imagine McDaniels having a prob with him staying.
There are pieces that will probably stay whether they go OC or DC as a coaching hire