Vienna & Budapest 12 night - should I split half and half or spend more time in Vienna?

I am taking my 78 old year mom to visit Vienna and Budapest during the first two week of May. We are staying twelve night. I am debating whether I should I split my trip evenly between the city? or is there more to do in Vienna than Budapest? I was think of doing 7 day in Vienna (including 1 day trip to Bratislava) and 5 (half day for transfer) day in Budapest. Considering we are not going to doing much on the day of landing and lost half a day on the transfer to Budapest, we would have 6 full days in Vienna and 5/4.5 day in Budapest.

We are not into hiking, party, drinking or luxury shopping (local souvenir is fine). We like to see architecture, stroll around the old town, eat local food, coffee, and look at local stuffs. My mom has high blood pressure, not sure if she can do the thermal bath, but I would like to try it.

Edit:

I am taking the trip at a slow pace, most like one big attraction (palace) per day. I am open for short day trip. Not going to do Salzburg as the commute is long for my mom's standard. Don't want to add another city. Changing 3 locations was too much for my mom. We visited three cities in Spain last time and although she didn't complaint, I call tell it had taken a toll on her. So going to keep is simpler this time.

I learned my lesson last trip that changing hotel reservation is like canceling a flight and booking at the current rate, meaning at a higher price most likely. Hence, I kind have to decide how to split the nights now. Adjusting hotel later on is a pain. How Expedia system works is not simply adding a day or subtracting a day. The system need to find the another available room with the same dates in order to adjust dates. What I can do is split the hotel reservation at Vienna and Budapest with an extra day on a separate reservation so when I need to cancel it does not affect the price on the rest of the nights.