I think that's right, the Bulls would most likely have not wanted to take on the salary from any player exchanged. Any Wigan player worth swapping would be on decent money and the funds may be needed elsewhere.

Wouldn't it have been due once our 2014 status was confirmed just after Easter?

I wouldn't be surprised.

It says "In addition to the sales consideration detailed above (the £150k), OK Bulls will make a further payment in the sum of £100,000 should the club retain it's SL status for the 2014 season".

However, given that the report was dated 9th July 2013 then I assume that it wasn't due prior to that as it makes no mention of it being overdue etc

Your uncle is wrong, no chance.

Absolutely right. Fozzie is not for sale - at any price.