Tithing Money for an Unbetrothed Sister

I am saving my tithes and my wife's for my sister's wedding. My sister is not yet engaged. The question is whether I can save the tithes for the wedding even though they are currently not being used for anything, and also whether it is possible to give all the tithe or only part of it, and if there is any other halakhic aspect to this matter. Thank you.

Shalom and good tidings!
It is permitted to save the tithes for your sister's wedding.
It is permissible and appropriate to keep all the tithes for the parents' expenses, as they take precedence over all other recipients of charity.
In the meantime, the money should be deposited in a Gemach (free-loan fund), so that it can be used for charity until it is used for your sister's wedding.