Sadly, Dad is no longer with us either, so I’m hanging on to it.
As he got older he started shrinking but liked his grey Craghopper Kiwi trousers (lightweight poly-cotton outdoor trousers). And I used to take them up for him in the legs so that he didn’t trip over. It was particularly badly done mainly because they tapered to the bottom and I when I turned them up inside the new hem material was a smaller diameter than the material I had to stitch it to - and it didn’t stretch! Still don’t know how to cope with that situation.
Welcome Andy, as others have said, this is a welcoming place, full of supporters and enablers.
For your hemming issue. Cut the trousers off at the length you want plus 1/2inch for seam allowance. Use a similar fabric from your stash (you know that sewists are required to have a stash don't you?
) , cut a facing the exact shape as the bottom of your trousers (two pieces if you want, then sew together to make a tube). Then you match up the bottom edge of the legs, and the shorter edge of the facing, right sides together, stitch around the leg hole with a 1/2 inch seam allowance. Turn the facing to the inside of the leg, fold in the edge, and then handstitch or machine sew the edge. Because your facing is shaped the same as the trouser leg, your facing should lay flat on the inside of the trouser leg, and give a nice finish. Remember to press seams as you go.