The second ability of Leyline of Hope applies just once to each life-gaining event, no matter how much life is gained. If you gain an amount of life "for each" of something or "equal to the number" of something, that life is gained as one event and Leyline of Hope's second ability applies only once.

If you control two Leylines of Hope and you would gain life, you gain that much life plus 2. A third Leyline of Hope has you gain that much life plus 3, and so on.

In a Two-Headed Giant game, life gained by your teammate won't cause Leyline of Hope's second ability to apply, even though it will cause your team's life total to increase.

A player's "opening hand" is the hand of cards the player has after all players have taken mulligans. If players have any cards in hand that allow actions to be taken with them from a player's opening hand, the starting player takes all such actions first in any order, followed by each other player in turn order. Then the first turn begins.

Because damage remains marked on creatures until the damage is removed as the turn ends, nonlethal damage dealt to creatures you control may become lethal if Leyline of Hope leaves the battlefield or if your life total drops below 7 life more than your starting life total.

Each creature with lifelink dealing combat damage causes a separate life-gaining event. For example, if two creatures you control with lifelink deal combat damage at the same time, Leyline of Hope's second ability will apply to those two events separately. However, if a single creature you control with lifelink deals combat damage to multiple permanents and/or players at the same time (perhaps because it has trample or was blocked by more than one creature), the ability will apply only once.