Loaning money to parents to help complete their cash offer

[Jon Christensen]

My parents are both retired. They recently signed a P&S offering cash for the house across the street from my sister with a 3 week closing (fast!). To come up with the cash that quickly they have to pull money out of their tax sheltered retirement accounts. Waiting until their current home sells is not an option.

To limit the tax hit they will take I would like to gift them $30k cash from my savings and $70k cash from my HELOC. When my parents' primary residence sells in the next few months they will return the cash, including any interest from the HELOC.

What are the implications of this transaction for me or my parents? Are there any legal or tax consequences? 

Thanks!