Regarding the turn at the top of P-Pans for the XLBs, I believe if they were to meet another bus they’d have to do a loop around where the 124 goes and back on route from there. Similar to what the 24s do at the Grange Loan if they meet a bus in the wrong place, just loop the 41 route.
The roads are quiet enough that it doesnt matter. The XLB's are only being used on 26's just now due to lockdown being eased and people going to the beach, although i can see them staying for a short time. They will eventually stop running on (at least Tranent 26's) and the frequency of the 26 will just be upped.
During normal operating conditions i.e not during a pandemic, the XLB's wouldnt run on tight roads, however it is required to maintain social distancing on various routes.
The tight turn in question is Ayres Wynd and if you think it's tight going left, imagine going right. I imagine this is what you're instigating by saying ("I believe if they were to meet another bus they’d have to do a loop around where the 124 goes and back on route from there.") The fencing thats on that corner would be taken out by tail swing and even then it probably get enough clearance on that corner due tight roads and ignorant drivers. Not to mention they'd have to miss a stop as turning onto (B1349) Station Road would be incredibly difficult, considering theres usually cars badly parked, as well as turning off of it onto Preston Road, not to mention (B1349) Station Road is a very tight road, due to previously mentioned parked cars. Property owners have been known to intentionally park badly to stop vans and trucks using that road.
I'm not saying it cant be done, im just saying it would be incredibly tight and probably wouldn't be allowed.
Lets be honest, the buses are probably having to go on the wrong side of the road to turn left onto Preston Road as even some standard and short length deckers do...