Ok so if you got let's say 4% (Wise) on USD, after five years with 6.5m you'll have got 1.3m in interest, so the house is basically rent-free. I wouldn't call 4% high interest as I've looked for high interest, but to cover the rent I see where you're coming from. I'm looking for around 10% on capital of €300k - to live off.
Facebook is great for getting info and advice, it's just plagued with morons who live on here and have nothing better to do than broadcast their unemployment, general ignorance, or signal their virtue. Unfortunately only good moderation can maintain standards in any given group. Moderators should be rewarded for their time and effort. It'd be worth paying a fee for some groups to keep the trolls out IMO.
A few people have mentioned you have to show the funds came from an overseas account which of course they did. That initial deposit is still visible in the bank book, a copy of which was provided. And that was acceptable for the previous renewals of my retirement visa. So perhaps I can go back to the bank and have them specifically state that these funds came from abroad and have not been withdrawn since... I should add that the individual at the reception has hinted at a 'way' to resolve the situation without having to transfer, and likewise for my child's education visa, so the solution may be just to bypass her and hand the application in to the clerks. It's not really feasible for me to do a visa run as I'm a single parent with a small child.