It would have been nice/the right thing to do
for the friend to share the profit for 2 of the
weld jobs with your husband.

I say bite the bullet and be gracious about the
the first 3 which your hubby
already agreed to weld.
If his friend wants any more jobs welded in the future
than your husband at that time can say he would
like to his share for his work and they can
come to an agreement.

JMHO since this friend has helped you out in the past.