I don't know which sentence is grammatically correct.
1 or 2 friends is enough.
1 or 2 friends are enough.
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To me, the singular/plural issue depends on what "enough" refers to; whether it is used in a quantitative or qualitative sense, or at least a countable or non-countable sense.
If "enough" means a sufficient quantity of people in a countable sense, it would be "are": "1 or 2 friends are enough to move the couch."
If "enough" means sufficiency for a qualitative criterion, it would be "is": "1 or 2 friends is enough to make me happy."
That said, I can think of an example that seems ambiguous:
"1 or 2 people are enough to feed a village of cannibals." This would be in the countable sense of a recipe: 1 bucket of potatoes, 3 bunches of carrots, and 1 or 2 people.
"1 or 2 people is enough to feed a village of cannibals." This would be in the non-count sense of the village having a sufficient amount of (non-countable) food (and it's really referring to people meat that has been divided up or consumed, rather than countable people at that point).
I changed "friends" to "people" because even cannibals don't eat their friends (well I'm just guessing on that point).
Both could be grammatically correct. It depends on the context in which it is said.
If the thought ends after 'enough' then is is correct. This could happen if, for example, the statement were the reply to the question "How many friends do you need in order to be happy?"
If the thought doesn't end there, and 'enough for some purpose' is implied, then are is correct. This would be the case if the statement were a reply to "How many friends do you need to help you carry your fridge downstairs?"
When we chat informally, there are a great many things we don't say because the situation makes the meaning clear to everyone present. Those unsaid things have an effect on the grammar of what we say, which in turn makes our meaning clearer to the people we're talking to. That makes it difficult to arrive at a straight answer when we isolate a fragment of conversation, as we're doing here.
"2 friends are enough" would mean that each of the '2 friends' is somehow 'enough' by themselves, like "[1 or] 2 apples [of the 35] are red."
However, 'enough' (as in the question) refers to the numerals/numbers only. Therefore: 'is'.
How many of the apples are red? 1 or 2 [apples] are red.
1 or 2 apples are red.
How many friends do you need? 1 or 2 [friends] is enough.
1 or 2 friends is enough.
You could also flip it around:
1 or 2 is enough friends.
1 or 2 are enough friends.
Or take a larger number:
300 friends is enough.
300 friends are enough.
That's enough friends.
Those are enough friends.
But for red apples it's different:
Those are red apples.
That's red apples.
So, 'red' and 'enough' are different kinds of words. I'll leave it to the specialists to explain it with more fancy terminology (likely: 'enough' as an adjective vs 'enough' as an adverb).
The problem here is you are not using a complete sentence.
"Having one or two friends is enough" -- that is really the complete thought. And that thought, "having something," does not require a plural verb.
"Having a house, a boat, a car, and a wife, is still not enough for me."
See? It's not the quantity of things that are listed in the sentence. The verb refers to "having a number of friends," not the "friends" quantity.
To put it another way: Working at three jobs is hard.
Three jobs are too many to have.