Can holes in a tank be fixed?

Yes, but tank has to be pressure tested afterwards to make sure it's airtight. No shortage of youtube vids on different types of tank repairs. You might also look into costs of replacement tanks, no sense repairing one if it's cheaper to replace it.

If those are rust holes I would not fix it.

If not to many clean use penny and clean good and use soldering IRON no open flames ,I did it on 50 chevy had 12 cents in it 5 years ago and still no leak