For your use, I would employ 'predecessor',

a. A person who comes before another person in time; an ancestor, a forefather, a forebear.

For the sense of 'individual ancestors',

I have 13 predecessors.

Or, similarly, I might use 'progenitor',

1. A person from whom another is descended; an ancestor, a forefather; a parent.

for that same sense:

I have 13 progenitors.

For the more general sense of 'ancestors', understanding your use of 'ancestor' to mean 'a position in the genealogical structure', I might use 'ascendant',

8. One who precedes in genealogical succession; an ancestor; a relative in the ascending line, whether lineal, as father, mother, or collateral, as uncle, great-uncle.

So in your second example:

I have 38 ascendants.

Note also that, depending on the purpose or nature of the genealogy, I might use 'propositus' rather than 'proband'. This is because the sense of 'proband' is usually restricted technically, as

Med. and Genetics. The individual with whom the investigation of a family for a genetic disorder or other inherited trait begins; the first member of a family to be diagnosed with a hereditary disease or trait.

'Propositus', on the other hand, is not restricted in technical use to a primary ancestor considered with reference to genetic disorders or inherited traits, but is more generally applied any individual viewed as the basis of a genealogy:

1. A person from whom a line of descent is derived; an individual from whom family relationships are calculated or on whom a genealogy or pedigree is based.

(All definitions from OED Online. Phrase emphasis in definitions of 'ascendant' and 'proband' is mine.)

For your use, I would employ 'predecessor',

a. A person who comes before another person in time; an ancestor, a forefather, a forebear.

For the sense of 'individual ancestors',

I have 13 predecessors.

Or, similarly, I might use 'progenitor',

1. A person from whom another is descended; an ancestor, a forefather; a parent.

For that same sense:

I have 13 progenitors.

For the more general sense of 'ancestors', understanding your use of 'ancestor' to mean 'a position in the genealogical structure', I might use 'ascendant',

8. One who precedes in genealogical succession; an ancestor; a relative in the ascending line, whether lineal, as father, mother, or collateral, as uncle, great-uncle.

So in your second example:

I have 38 ascendants.

While the context may make the distinctions between the terms you use evident, it might also be advisable to make explicit the distinction between 'predecessors' or 'progenitors' in the sense of 'individual ancestors' and 'ascendants' in the sense of 'a position in the genealogical tree'.

Note also that, depending on the purpose or nature of the genealogy, I might use 'propositus' rather than 'proband'. This is because the sense of 'proband' is usually restricted technically, as

Med. and Genetics. The individual with whom the investigation of a family for a genetic disorder or other inherited trait begins; the first member of a family to be diagnosed with a hereditary disease or trait.

'Propositus', on the other hand, is not restricted in technical use to a primary ancestor considered with reference to genetic disorders or inherited traits, but is more generally applied to any individual viewed as the basis of a genealogy:

1. A person from whom a line of descent is derived; an individual from whom family relationships are calculated or on whom a genealogy or pedigree is based.

(All definitions from OED Online. Phrase emphasis in definitions of 'ascendant' and 'proband' is mine.)