I find, and my colleagues all around the country report, that too often people set up lifetime trusts without funding them. They don't realize that merely creating a trust isn't enough, and that they need to follow the necessary steps to formally "fund" the trust. Funding a trust means actually placing money or other assets in a trust, generally by re-titling them in the name of the trust. To make sure that a living trust is funded during a person's lifetime you usually start the trust with ten dollars and then add other assets when you are ready. Additional assets may be added during your lifetime and/or assets may pour-over into the trust at death through your will. What you do to create a funding plan is based on advice from your attorney and any financial advisors.
It also is possible (but not required) to provide that other people can contribute assets to the trust you set up. Those contributed assets will be divided among the trust beneficiaries in whatever way you determine when you set up the trust terms. The third party additions to the trust cannot change the trust terms or add additional terms, because it is your trust. You will already have established all of the terms, and someone adding to the trust if you allow additions will know what terms you have selected. You do not have to allow a third party to add to the trust, and the trust can contain whatever terms you decide on with your attorney as the best course for you. Whenever you are doing estate planning, no matter how large or how small your estate, it should reflect your goals and your values, and it is your wishes that count.