Quadathlon- hiking, swimming, running and cycling

A few months ago, i couldn’t ride a bike or run long distances due to injuries and problems i had throughout my childhood, but now with a lot of support, my confidence had rapidly grown and i am looking to complete 4 challenges in order to raise money for a couple of charities close to my heart. My challenges i’ve set myself are- the 3 peaks challenge (Snowdon, Ben Nevis and Scafell Pike) within 24 hours, cycling 100 miles, swimming 1 mile in a pool (52 lengths) and running a half marathon. Does anyone have any training methods they have that could help me keep in shape and build endurance ready for these challenges?