Knot their sons omega by: Sage Relleanne

Xenia doesn’t have a choice.
Omegas never do.

With her Alpha gone and his brother intent to claim her, Xenia is forced to endure her heat under clinical supervision—safe, controlled, and anonymous.

She expects that to be the end of it, but a month later an impossible word stares up at her.

Armed with her mysterious Alpha’s name, she goes in search of him…only to find his three unmated fathers and the news that their son is dead.

Heartbroken as her grief compounds two-fold, she tries to flee, but a treacherous snowstorm forces her into their home and as the time passes, into their hearts.
Unfortunately, as the snow begins to melt, she realizes the true danger has yet to come.

This is an omegaverse why choose snowed-in standalone