Second (elite) guest joining mid-stay
 

My brother has a booking for a Sheraton in NYC for 10 nights, he has no status with Marriott.
I will join him (as Titanium) mid-stay and share the room for the last 4-5 nights.

What's the best 'strategy' to get Titanium benefits (incl. potential upgrade), at least for the 4-5 nights I'll stay there?

If his name is on the reservation and you are sharing his room, I doubt you will get anything as you are his guest. If you are on your own reservation, the normal chances. We have had very little luck with room upgrades in NYC.

Split the booking in two. Have the first one on his name and second one on yours.

this

anything else is "how do I angleshoot stuff I'm not entitled to?"

My husband is gold. I am titanium. He has an 85K award cert from a credit card. When we use it, we have whatever benefits accrue to his status, not to mine.

It is YMMV. It does not hurt to ask and/or to tell the hotel the 'Titanium customer' is the second guest. I have gotten benis before on more than 1 occasion.

If we book two nights, first night with my FNA, and second night with my wife's FNA, then we'd get (my) elite benefit for both nights.

We had also done a single night with my wife's FNA, and let the hotel know her husband that's staying with her is elite, we had also received the benefit. But I understand it's YMMV.

Do you both have at least Platinum Elite status?

For a room booked, occupied, and paid by the elite member, you get free DAILY (not just one day) breakfast, regardless of the length of stay as a Welcome Gift or as part of Lounge Access (or alternative) at brands that offer one of these benefits. For a quick overview of the qualifying brands, see the wiki at the beginning of the sticky "FAQ : Marriott's 'breakfast offering' explained" thread.

But if a stay is booked with an FNA (or as a regular paid stay) by a member who is not at least Platinum Elite or above, then the Terms & Conditions do not call for free breakfast. A hotel might provide it anyway if another guest in the room qualifies, but is not required to do so.

Exactly. It's YMMV. The trend is that hotels are getting stingier, not more generous. But you MIGHT get elite benefts anyway, either because management at that hotel knows that treating elite guests well is good business or because the front desk doesn't know what the Terms & Conditions call for.

My wife does not have elite status. That's why I said I know it's YMMV (about getting elite benefit booked under my wife)