If a court grants dependant support, does that reduce what other beneficiaries receive from the estate?

Generally, yes. A dependant support award is paid out of the estate, so unless the estate has some untouched source of funds, ordering support usually means less is left for the beneficiaries named in the will or entitled on intestacy. Ontario courts have discretion in deciding exactly where that reduction falls — support can be charged against the residue of the estate, against specific gifts, or allocated in whatever way the court finds fair given the will's structure and the people involved.

This is one of the reasons dependant support claims are often contested by other beneficiaries, not just the estate trustee — an award that helps a dependant necessarily comes at someone else's expense within the same estate. Courts try to balance the qualifying dependant's genuine support needs against the deceased's testamentary wishes and the interests of the other beneficiaries, but they aren't required to protect any particular gift or beneficiary from being affected. Anyone affected by this kind of claim, on either side, should get legal advice on how an award is likely to be structured in their situation.