Hi I am in the Philippines and I live in the Central Visayans (Bohol) and there are 7000 islands in the Philippines and about 1000 islands are populated.
There may be records in one region of part Manila City Hall. I don't believe these records (if any exist) will be on line and it would need a personal visit the the particular city hall where the deaths were reported.
Unless it was murder or a drowning I doubt you will bottom the cause of death (if they both died in the Philippines) as even today an autopsy is not held unless an individual family will pay the cost.
Maybe you have the following information already?
I did find this Australian newspaper article as follows in family announcements:
Bell's Life in Sydney and Sporting Reviewer (NSW) Sat 7th Sept. 1850
" DIED.
At Manila, in April last, in the 25th year of
his age, Mr. George Brown, for many years in
the employ of Mr. Richard Dawson, iron-
founder, of this city.
At the same place, in May, in the 23rd year
of her age, Mrs. Brown, wife of the above, and
eldest daughter of the late Mr. Edward Wood-
hart, of Phillip-street, in this city. "
Andy_T