Wild Magic sorcerers get the Bend Luck feature at 6th level (PHB, p. 103):

Starting at 6th level, you have the ability to twist fate using your wild magic. When another creature you can see makes an attack roll, an ability check, or a saving throw, you can use your reaction and spend 2 sorcery points to roll 1d4 and apply the number rolled as a bonus or penalty (your choice) to the creature’s roll. You can do so after the creature rolls but before any effects of the roll occur.

Let's say Rico the Wild Magic Sorcerer has a simulacrum, Ricotwo (obtained via a Wish spell). Rico sees Bob, his friend, make a difficult saving throw, and wants both him and his simulacrum to use Bend Luck to add not 1, but 2d4 to Bob's roll in total.

Can more than one instance of Bend Luck be applied to the same roll?

No. The most potent effect is active.

This is the same effect, the most potent effect will be applied. Roll the d4 twice and take whichever bonus is higher. Only one effect can be applied at any time, regardless of the number of ways that try to apply the effect.

DMG errata version 2.0 page 1:

Combining Game Effects (p. 252). This is a new subsection at the end
of the “Combat” section:

Different game features can affect a target at the same time. But when
two or more game features have the same name, only the effects of one
of them—the most potent one—apply while the durations of the effects
overlap. For example, if a target is ignited by a fire elemental’s
Fire Form trait, the ongoing fire damage doesn’t increase if the
burning target is subjected to that trait again. Game features include
spells, class features, feats, racial traits, monster abilities, and
magic items. See the related rule in the “Combining Magical Effects”
section of chapter 10 in the Player’s Handbook.

Yes, but it won't work like that

You can apply two Bend Luck features to a single roll, but they won't stack. Instead, you would take the 'most potent' one, which in the case of two positive increases is the larger of the two dies; essentially the roll of the d4 would be made with advantage.

This is because, according to the DMG errata (first page, right hand side), game features with the same name don't stack:

Combining Game Effects (p. 252). This is a new subsection at
the end of the “Combat” section:

Different game features can affect a target at the same time. But when two or more game features have the same name, only the effects of one of them—the most potent one—apply while the durations of the effects overlap. For example, if a target is ignited by a fire elemental’s Fire Form trait, the ongoing fire damage doesn’t increase if the burning target is subjected to that trait again. Game features include spells, class features, feats, racial traits, monster abilities, and magic items. See the related rule in the “Combining Magical Effects” section of chapter 10 in the Player’s Handbook.

Note as well that if Rico had an evil twin, Ricothree, who sought to make Bob fail the saving throw determining which is more potent is somewhat less natural-- you still take the highest rolled number but it now is important to determine whether that number is a bonus or a penalty: only one of them applies. If the same number is rolled the GM must determine whether a bonus or a penalty is more potent, all else being equal, and should they decide that there is no inherent difference in potency the resolution is entirely unclear.

Yes, multiple instances of Bend Luck can apply

Multiple sorcerers applying their Bend Luck to a roll as a reaction can both successfully apply their modifier to the roll. Each time one is applied, it is applied as a bonus or penalty to the roll.

The "Combining Magical Effects" section does not apply

...apply while the durations of the effects overlap...

Overlapping duration is a requirement for the combining magical effects rule. There is no duration for Bend Luck, so that section does not apply here.