When they passed it went to my mom and her 4 siblings.

@stevenwilson made a suggestion I agree with. that is how my mother started private lending 35 years ago, she lent to her younger siblings (bank then rates were higher, so she saved her siblings some money, but also put her money to work)

My mother died last year and left our summer cottage in a trust consisting of myself and 5 siblings.

Between the siblings, they decided one brother was going to move in and buy out the other 2.

Unlike leads you can order online from a generic website, I can guarantee that the leads I pull are fresh (60 days or less), off market, and I use a ranking system to determine which sellers are most motivated based off of factors such as the executor of the property living in a different state and the amount of siblings the house has been inherited by.

I told my parents and 4 siblings, everyone thought I was nuts.  

In your position, maybe starting by communicating your ideas to the 3 siblings tied to the property would be a good place to start?

As the family started using it less my siblings and I convinced them to look into listing it as a short term rental.

If you have a spouse, child, grandchild, parent, sibling or grandparent in the military.

If you're confident it would sell and you can do it quickly, see if she can get a line of credit to borrow from or if the wedding is far enough away and the house will be renovated and sold, talk to your fiancé or siblings.