It's not 'mast' as the last two lines are:
And to my son Molton the B? if their should be out if not
to buy him out at 4 or 5 pounds value he having made free
with more than his share.
I'm not sure about the 'Boate' (?). It's odd that he refers to his son merely as Molton, but I think it must be asking him to sort out the money if things don't work out for the others.
Richard