Dreading a family gathering

Among the ways the Buddha gives for removing resentment toward a particular person, one is simply to stop paying them attention, which is worth remembering when an uncle starts. The others are love, compassion or equanimity toward them, and the reflection that their deeds are their own. There is also the choice not to accept what is offered in anger, so that it stays with the one who offered it. None of this asks you to feel nothing. For the rehearsal in the weeks before, a short set of verses advises against reaching for a future that has not yet come. The canon's test for speech — true, beneficial, and well timed — can decide ahead of time which conversations are worth having. If you have stopped drinking, the Sigālaka Sutta gives the drawbacks of habitual drinking entirely in terms of this life, and your reasons need no defending to anyone. What the suttas do not do is make you go. Whether to attend, for how long, and with what way out is yours to decide.

What the suttas say

“Mendicants, a mendicant should use these five ways to completely get rid of resentment when it has arisen toward anyone. What five? You should develop love for an individual you resent. That’s how to get rid of resentment for that individual. You should develop compassion for an individual you resent. … You should develop equanimity for an individual you resent. … You should disregard an individual you resent, paying no attention to them. … You should focus on the ownership of deeds regarding that individual: ‘This venerable is the owner of their deeds and heir to their deeds. Deeds are their womb, their relative, and their refuge. They shall be the heir of whatever deeds they do, whether good or bad.’ That’s how to get rid of resentment for that individual. A mendicant should use these five ways to completely get rid of resentment when it has arisen toward anyone.”
A practical list — love, compassion, equanimity, not attending, reflecting on kamma.
Where this stops: Reflecting that people own their deeds is never a way to call someone's misfortune their kamma, and putting down resentment is never a reason to stay near someone who keeps doing harm.
AN 5.161:1.1–1.15 · Getting Rid of Resentment (1st)
“In the same way, prince, the Realized One does not utter speech that he knows to be untrue, false, and pointless, and which is disliked by others. The Realized One does not utter speech that he knows to be true and correct, but which is harmful and disliked by others. The Realized One knows the right time to speak so as to explain what he knows to be true, correct, and beneficial, but which is disliked by others. The Realized One does not utter speech that he knows to be untrue, false, and pointless, but which is liked by others. The Realized One does not utter speech that he knows to be true and correct, but which is harmful, even if it is liked by others. The Realized One knows the right time to speak so as to explain what he knows to be true, correct, and beneficial, and which is liked by others. Why is that? Because the Realized One has sympathy for sentient beings.”
Prince Abhaya — the test for whether and when to say a hard thing.
Where this stops: For deciding whether and when to say one particular hard thing; it does not judge a relationship as a whole, and it is not a reason to say nothing. Nor does it mean anyone owes another person news about their own body, health or pregnancy, or should speak when speaking would put them at risk.
MN 58:8.1–8.8 · With Prince Abhaya
“Do you then serve them with fresh and cooked foods and savories?” “Sometimes I do.” “But if they don’t accept it, brahmin, who does it belong to?” “In that case it still belongs to me.” In the same way, brahmin, when you abuse, harass, and attack us who do not abuse, harass, and attack, we don’t accept it. It still belongs to you, brahmin, it still belongs to you! Someone who, when abused, harassed, and attacked, abuses, harasses, and attacks in return is said to eat the food and have a reaction to it. But we neither eat your food nor do we have a reaction to it.
Declining to take in what someone hurls at you in anger, the way a guest can leave a dish untouched.
Where this stops: Concerns how abuse is received inwardly; it is no reason to stay where someone keeps abusing you.
SN 7.2:2.5–3.2 · With Bhāradvāja the Rude
There are these six drawbacks of habitually consuming intoxicants of beer, wine, and liquor. Immediate loss of wealth, promotion of quarrels, susceptibility to illness, disrepute, indecent exposure; and weakened wisdom is the sixth thing. These are the six drawbacks of habitually consuming intoxicants of beer, wine, and liquor.
Six drawbacks of habitual drinking, given to a young householder entirely in terms of this life — wasted money, quarrels, illness, a bad name, exposing oneself, and a weakening of wisdom.
Where this stops: Said of habitual drinking and offered as a list for reflection; it is not a diagnosis, and someone whose drinking has become a dependency needs more than a list.
DN 31:8.1–8.3 · Advice to Sigālaka
Don’t run back to the past, don’t anticipate the future. What’s past is left behind, the future has not arrived; and any present phenomenon you clearly discern in every case. The unfaltering, the unshakable: having known that, foster it.
The Bhaddekaratta verses — letting go of the chase after what is gone and what has not yet come, in favour of what is here.
Where this stops: The verses go on to urge effort today, since no one knows whether death comes tomorrow; they are about where attention goes, not a dismissal of planning or of a past that still needs repair.
MN 131:3.1–3.8 · One Fine Night

Bring your own situation.