i think yes for all 3 qs. i don hav the game but i saw my fren playin it. i think u have to meet certain requirements before u can join two cards.

you need polymorphism i think then the Fusion Card and the two monster that is required by the Fusion Card

Fusion card @@

i think its 1 monster card on the field.. then u use the fusion card, choose a
monster card from your hand.. and cantum wit the monster card on the field

i saw how yugi did tat.. @@ terus come out kimaya

Continue form the above
FUSION DECK
A Fusion Deck is a group of Fusion Monster Cards that result from a successful Fusion. When a Fusion is performed, Fusion Monsters are not randomly drawn, but selected from the Fusion Deck. The Fusion Deck should always be kept separate from the Deck, and placed face-down in the Fusion Deck Zone of the Duel Field. Remember that the cards of the Fusion Deck are NOT counted in the 40 card minimum limit of the deck.

C. Effect Monster Cards
Monster Cards that possess magical effects are referred to as Effect Monster Cards. The broad range of Effects are divided into the types listed. For details regarding the effects, refer to the instructions printed on each individual card. Effect Monster Cards are color-coded ORANGE.

I. Flip
The monster's effect is activated when the card is flipped from face-down to face-up. The effect is also activated if the card is flipped face-up as a result of a Magic or Trap card, or another monster's attack.
II. Continuous Effect
As long as this Monster Card is face-up on the field, its effect remains active. When the monster is turned face-down, its effect is no longer active.
III. Cost Effect
You must discard your hand or pay Life Points in order to activate this card. Costs vary from card to card so be sure to read the instructions printed on each card.
IV. Trigger Effect
These cards are activated when you inflict Direct Damage to an opponent's Life Points, or when you have fulfilled a specific requirement indicated on the card itself.
V. Multi-Trigger Effect
These are special Effect Monster Cards that you can activate even if it is your opponent's turn.