Fix up to learn if you like, but don't spend much money - those bikes (or bikes very similar) can be purchased for less than $100 each. Fixing up without replacing many parts will teach you more than just buying and installing new.

(Note that I said they 'can' be purchased. I did not say they 'should' be purchased.)

Also - Some of the parts you were talking about buying - specifically the Alivio cranks and bottom bracket - will not fit on your two bikes as they use a different bottom bracket and crank design that is not compatible with good quality stuff.

Also - Free bikes are seldom worth the price.