en_tn_condensed/gen/26/18.md

Isaac dug out

Here "Isaac" stands for Isaac and his servants. Alternate translation: "Isaac and his servants dug out" (See: rc://en/ta/man/jit/figs-synecdoche)

which they had dug

"which Abraham's servants had dug"

in the days of Abraham his father

"during his father Abraham's lifetime" or "when Abraham, his father, was living"

The Philistines had stopped them up

This was the reason that Isaac dug them out. Possible ways to translate this are: 1) Since this happened first, this sentence can come before the sentence about Isaac digging them out, as in the UDB. or 2) This sentence can start with "Isaac did this because the Philistines had stopped them up." (See: rc://en/ta/man/jit/figs-events)

had stopped them up

"had filled them with earth"