Manila is the hardest of these three cities to bring an older parent to, and pretending otherwise would waste your time. Plan it properly and it works; plan it like a European city break and it will defeat you by day two.
Start with the rail, because the picture is uneven. There are three urban lines — LRT-1, LRT-2 and MRT-3 — they interchange badly with each other, and they do not reach most of the places you will actually want to go. LRT-2 is the exception and was deliberately built to answer complaints about the lack of universal access on the earlier lines: all its stations have lifts between concourse and platform, though not every station has one on both sides of the road, so you can arrive at the right station on the wrong side and find yourself stuck. LRT-1 and MRT-3 are older elevated lines reached by long flights of stairs, and MRT-3 in particular runs so crowded at peak that the queue backs down the staircase. Do not plan to move a frail parent through MRT-3.
The streets are the bigger problem. Outside BGC and the better parts of Makati, sidewalks are narrow, broken, blocked by parked vehicles and vendors, or simply not there, and crossing a major road like EDSA means a footbridge with stairs. Intramuros, which you will want to see, is cobblestone throughout — charming and genuinely punishing on hips and on wheels. The kalesa carriages and the rented bambikes at the gate exist for exactly this and are the right call, not a defeat. And the traffic is among the worst in the world: two commitments in one day at opposite ends of the metro is an unrealistic plan, and it is the traffic rather than any staircase that will finish an eighty-year-old off. Heat compounds it — hot and humid all year, worst from March to May before the rains, and the wet season from roughly June to November brings typhoons that close things at no notice.
Now the genuine advantages, because they are real. The Philippines treats elderly people and children as a structural priority, not just a social one: there are dedicated senior citizen and persons-with-disability lanes at malls, banks, pharmacies and government counters, and staff will wave a visibly elderly visitor into them. The legally mandated senior discount attaches to Philippine-issued senior ID, so a visiting Canadian parent will not usually get the price break, but the priority queue is a courtesy that is extended anyway and it saves a great deal of standing. The malls are vast, genuinely cold, and equipped with clean toilets and nursing rooms, and the big ones generally keep wheelchairs on loan at the concierge or customer service desk — ask at SM Mall of Asia, Greenbelt or Megamall. Use them as your afternoon base without embarrassment.
The single biggest advantage over Jakarta is language. English is everywhere and near-universal, so an older relative separated from the group can ask literally anyone for help and be understood. Finally, the airport: NAIA is congested, its terminals are separate buildings, and moving between them means going out into landside traffic. Build a long buffer, and arrange a pickup in advance rather than making an elderly traveller negotiate a taxi queue at two in the morning. Manila runs twelve hours ahead of Toronto in summer, a straight flip of the clock, so give them a recovery day before anything is scheduled.