Ikiwa is another word for "if". It's actually simply a verb ... the verb "to be", kuwa with the subject prefix i- for class 9 (singular N class) "it" and the ki prefix. On its own, it means "if it is". So this sentence is like 'if-it-is they-will-come we-will-buy gift(s)'.
Kama also means "like" (as in "similar to").
Here Ikiwa is followed by "watakuja", in the future, not conditional. AGreatUserName explains that ikiwa is actually a verb, so the conditional is already there. However, other sentences hve ikiwa followed by another verb in the conditional. How do we know whether the verb following ikiwa should be future or conditional?
Ikiwa - again something without sense. " If it is they will come, we will buy the gift." The most funny is that in " Notes and tips" is no one word about " ikiwa" nor about these every freaks given before. For keep the meaning of the sentence in translation is well to write - Kama watakuja, tutanunua zawadi / Wakija, tutanunua zawadi.