to is not required following sent. to send (as well as to give, to lend, to feed, etc.) can take an indirect object (without a preposition) as well as a direct object. If there is only one object, then it’s a direct object* - the item that is actually being sent, as in:
He sent a gift
But if there are two, then the order is [indirect object - person receiving the item being sent] [direct object - the item being sent], as in
He sent me a gift.
I don’t think to would be incorrect in this context, but a prepositional phrase normally follows a direct object, so this would be better:
He sent a gift to me.
Your first example sounds better without the to.
As for your second example, neither sounds right to me. As with to send, if to present takes one object with no preposition, it is assumed to be a direct object. So “presenting you guys” sounds like “you guys” are being presented- that is wrong.
“Presenting to you guys” is grammatical but not idiomatic. Normally when you say you are presenting something, it is understood that “you guys” is the audience. You could simply say:
Presenting the trailer of the film.
This is more idiomatic. You could tack on “to you guys” at the end of that sentence but it’s not necessary.
*EDITED to note- what I said about a verb that can take both an indirect object (with no required preposition) and a direct object - that it takes a direct object if there is only one object specified- is not true for all verbs. “I fed a fish” means “I gave food to a fish”, so in this case a fish is the indirect object. However, “to send” must take a direct object and if only one object is used, it has to be a direct object. “She sent me” means she made me go somewhere- so me is the direct object.