In regards to Britain going fascists do not say no. The loss of face to Germany would of rocked the British politics and a more right wing party could of emerged.
Because British defeat in Suez in the Napoleonic Wars the loss of India and Singapore all contributed to the rise of a major far-right party correct? Even so Said far-right party in your circumstances would likely be vehemently anti-german so your point still doesn't stand
As for the Iberian peninsula I think that unlike Britain Germany not need to build a fleet and battle RN to invade. All they had to do is send their troops over the Pyrenees mountains. So unless the US launches a surprise invasion of the Iberian peninsula like they did North Africa the two countries open themselves up to invasion from Germany.
Yes and Germany would likely find Spain far more useful as a conduit to international trade instead of you know invading and pacifying and feeding a major war-torn country led by a friendly ruler
Neither would Portugal and Spain trust the US.
They'd trust America a hell of lot more than anyone would trust Germany with an clear record of backstabbing and breaking every treaty they have ever signed