Remove him through some part of the Act of Succession? Cut him off from any funds and leave him poor as dirt (power of the purse)?
Behead him if they want? Wouldn't exactly be the first time.
The Monarch of the United Kingdom is a Bully Pulpit, that's it. No actual power. Doesn't even get to write Their own address to Parliament. They do what they are directed, smile, provide a touchstone of tradition, and may even have some soft power. The real Power is Commons, has been since the Glorious Revolution, although the full effects didn't get set in stone until the mid-1850s.
Actually this is misconstrued. The British Crown has a lot of theoretical power at its disposal. There's no law that says the PM must be from the majority party in Parliament, for example, nor is there any law that says the Sovereign can't dismiss ministers at will. Also Parliament never deposed a monarch, that's a common misconception. They voted to interpret James II's actions while fleeing the Kingdom as an abdication but they never point blank said that "by Parliament's power James II is deposed". Sure if Queen Elizabeth decided tomorrow to dissolve Parliament, dismiss the government and retake the crown estate there would be a huge upset, but
legally she can.
So in theory Edward VIII could marry Wallis without Parliament doing jack about it. People tend to forget that Edward VIII was popular among the working and lower classes thanks to the famous "Something must be done" line. Plus Churchill supported him as well, so if Edward had stayed we might see an earlier return to power for him as well.
Yes doing so would cause a government crisis, but not to the paralyzing extent that Edward's ministers wanted him to think. The government falls, and if Edward isn't able to get someone else to form a ministry than Parliament would dissolve and it goes to a general election. However, I wonder if the MPs would want to risk calling an election at that time. It would basically be a de facto referendum on Edward's marriage and it could swing public opinion in his favor, basically making the conservative party look like fools.
The real problem would be in the dominions, whose governments also threatened to resign if the King went ahead and married Wallis (although again I wonder push comes to shove how many would actually resign and how many would back down) and with the Anglican Church, which refused to recognize divorce. Which is funny considering that the modern Church of England was founded by royal divorce.
Basically Edward would be in a difficult place if he married Wallis and refused to abdicate, but if he played his cards right he could come out ahead.