So, Ba is divalent. This means that each Ba(OH)2 requires two I in order to produce one BaI2 molecule.
The two hydrogens from the 2 HI molecules will combine with 2 OH of Ba(OH)2 forming 2 water (H2O) molecules.
The equation which illustrates this reaction in as follows:
2 HI (aq) + Ba(OH)2 (s) ........> BaI2 (aq) + 2 H2O (l)
where:
aq refers to aqueous state
s refers to solid state and
l refers to liquid state.
