I see you've already had some great advice and support from bec on your other threadRe: 5 month old sleep issues
There isn't much I could add to that really.
It's totally normal for a LO this age to still have a night feed and for there to be more than one during a growth spurt (or perhaps due to teething if there is pain) so I would continue to feed at night, many LOs take a dream feed but if yours doesn't then just feed at whatever time he wakes taking that it has been at least 3hrs since last feed.
With the unpredictable morning WU time really I only see two options:
1. treat as NW and stay with him resettling until 7am - but this will disturb your other child and there is no guarantee that your LO will sleep until 7am anyway
2. get him up whenever he wakes (say 5.30) and start the day - this is the easiest and quietest option IMO and less chance of disturbing your other child.
I'd take option 2 if it was me and then gradually shift the whole day so that you eventually bring WU and BT later to fit in the 11hr night he can do (rather than expecting a 12 hr night). Bec gave you some great advice as to how to move things on by shifting the first nap of the day gradually later. As Bec has said you are likely approaching the 3-2 nap drop and you could perhaps hold on to a short CN a little while to help you bridge the gap between nap 2 and BT as you gradually move the naps later.
During a nap drop it is quite normal for BT to end up a bit later than you'd hope for and a shorter night until the nap being dropped has fully gone, then BT can move earlier again, but only to a time when you are offering an appropriate length of night for your LO otherwise LO ends up waking earlier than you want.
With feeds it's normal for there to be a period of 3.5hr E or for the E to be at slightly different times depending on nap length. Whatever time the E comes towards the end of the day do another at BT regardless of it being less than 3hrs.
If LO is not so keen on the morning feed you could wait perhaps 30 mins before offering the feed - some LOs just don't like to eat as soon as they wake. I think mine waited an hour before he could have his milk after morning WU (even after dropping all NFs, he was just always that way).
I thin otherwise maybe re-read the advice from Bec as she's covered pretty much everything really and I am only repeating what she's said.
Nap drops and changes in routine are typically a tricky time - you'll get through it