With regards to tipping the wheelchair assistant, bear in mind that they may expect a tip per chair and per leg, ie a tip for each assistant who helps you and your wife to the lounge and the same again to the aircraft. You might want to make sure that you have enough dollars in cash with you.
I have used the assistants in the past and felt a bit “mugged” by the end of the experience. It was a relatively short distance with no undue waits. I collected luggage and pushed that while the skycap pushed my son’s wheelchair. At the last moment, he called over a colleague who literally opened one door for us and they both expected to be tipped $20 (they told me that was the minimum!).
It’s really good that some people have had much more positive experiences.