You still need to confirm all this, but...
When grandmother gifted her ownership in the house to the trust, the trust owned 1/2 and each of her children owned 1/6th. When your mother and your uncle passed away, their respective 1/6th should have been disposed of through probate according to their respective wills or the MA intestate succession statutes. (Which means that your deceased uncle's widow likely does have an ownership interest.)
Now that grandmother has passed away, your surviving uncle is the trustee and has the duty to administer the trust according to the trust's instructions. (Your uncle does not "own" the trust.) According to what you have posted, your surviving uncle receives 1/3 of the trust assets, your deceased uncle's children receive 1/3, and your deceased mother's children receive 1/3. That applies not only to the share of the house that was titled to the trust, but any other assets that were titled to the trust.
Which would mean that your surviving uncle ends up owning 1/2 of the house, with the remaining 1/2 share scattered among several grandchildren (and probably the deceased uncle's widow) in varying fractions.
The provisions of grandmother's will apply only to any of her assets that were not titled to the trust.