Overload doesn't change when you can cast the spell.

Kindred is a card type that allows noncreature cards to have creature types. For example, Echoes of Eternity is an Eldrazi (although not a creature) while on the battlefield and an Eldrazi card (although not a creature card) in zones other than the battlefield.

If you don't pay the overload cost of a spell, that spell will have a single target. If you pay the overload cost, the spell won't have any targets.

To determine the total cost of a spell, start with the mana cost or alternative cost you're paying (such as an overload cost), add any cost increases, then apply any cost reductions. The mana value of the spell is determined by only its mana cost, no matter what the total cost to cast that spell was.

Because a spell with overload doesn't target when its overload cost is paid, it may affect permanents with hexproof or with protection from the appropriate color.

Effects that cause you to pay more or less for a spell will cause you to pay that much more or less while casting it for its overload cost, too.

If you are instructed to cast a spell with overload "without paying its mana cost," you can't choose to pay its overload cost instead.

While it appears only on cards that already have other card types, kindred is a card type and will be counted by effects that refer to the number of card types among cards in a zone.