I'd just keep an eye on him ski it could be silent reflux, or it could just be him choking a bit as you say. I think reflux can start any time around now, if I remember the kellymom site right. Though I think it also tends to get better at about 6 months. Perhaps it's reflux from something he's eaten though? Are you weaning him yet?
In laws seem like a bit of a nightmare all round.. They do make for fun reading though ;) As long as you can ignore the annoying stuff and laugh at the stupid stuff you hopefully won't go mad.
DSs naps have only had a routine the past few days. I just hear lots of people say they're LOs aren't allowed to sleep past 4pm. DS will sometimes happily sleep on me till 6pm, and usually doesn't want to wake up from his afternoon nap at all. So I'm wondering if its more like his first 'night' sleep rather than a nap. He's generally overtired and shouty by 7 even if he slept till 5 or 6. If I wake him at 4 he's overtired by around 5. 
Spotty sounds like a lovely day. Lots if the towns round here have a village "day" which is a local holiday for all the schools and businesses. I've never been to one, but quite fancy it. Not sure if its a Scottish thing or a town/village thing?
We failed at self settling tonight. I've had a couple of successful evenings where I feed him, he pulls of happy and awake so I let him lay there for 30 mins or so till he falls asleep. Tonight he was happy for 30 mins before crying inconsolably just as he was starting to look properly sleepy. I'll try again tomorrow later I guess.