The use of Ash's house might be a gift of $3,333.33 per month ($40,000 per year), but not necessarily.
The IRS often treats the privilege of allowing your friends and family to use property you own for free (especially when you are there at the same time) as a benefit to the owner of the property rather than a gift to the friends and family. This applies not only to the residence, but to use of separately owned property of the residents.
Each donor has an annual exclusion from gift and estate taxation of $17,000 per person, per year.
So, even if the right to live rent free in the property were treated as a gift of $40,000 per year, per person, the gift that would be reported on IRS Form 709 (a gift tax return) by Ash, would be $13,000 for Bret and $13,000 for Charlie (which would counts against a $12.92 million lifetime exclusion from gift and estate taxation for Ash, that grows annually with inflation).
Property purchased with joint funds owned by all who have contributed, when they are not spouses, is usually deemed to be a tenancy in common with ownership proportionate to the share of monetary contribution, and that is the legal basis for splitting up the proceeds if tenancy-in-common property is sold. Tenancy-in-common ownership affords all owners, regardless of their percentage interest, an unlimited right to use the undivided whole of the property. So the use of the jointly owned property and the purchases of the jointly owned property wouldn't necessarily constitute a gift at all for income tax and gift tax purposes.
This arrangement, as a bona fide expense sharing arrangement negotiated at arms length, wouldn't give rise to income.
Also, if any of these transaction were deemed a gift from the person contributing more than they get back to the total arrangement (probably Ash), rather than just a sharing of expenses in an unequal but fair way, gifts received by Bret and/or Charlie would not taxable income, pursuant to Internal Revenue Code Section 102. The gift tax system is in lieu of income taxation on gifts.