is the Hebrew rule of grammar always consistent when it lays down the rule that "no two shevas begin a word?" For example, Brashith (Genesis) 27.28 uses the vav sheva followed by a yud sheva. Shouldn't this be read kri (pronounced) vav patach "vav hahipuch" rather than read as written k'tiv vav sheva (vav hachibur)?
וְיִתֶּן is a jussive, the translation therefore "May He (G'd) give" (and not: He will give)
There is (kind of) one exception to that rule, but ויתן is not it. It's in Haazinu 32:5:
הַ לְיְהוָה תִּגְמְלוּ-זֹאת
(I say "kind of" because ה לה' is read as one word.)