Visiting China soon! Need a little bit of advice :)

I (F18) will be traveling to China soon with my cousin (M18) and our grandparents (75+). We’ll be visiting Shanghai, and while it will be the first time for my cousin and me, our grandparents have been there before—though it was a long time ago.

I’m still researching how everything works there, so I’d love any tips or important things to keep in mind. We’re from the Netherlands, and as far as I know, we don’t need a visa for our trip in March.

I’ve heard that WeChat Pay and Alipay are the main payment methods and that cash is rarely used anymore. Which one would be better for us to use as foreigners?

Also, I’d appreciate any recommendations for reasonably priced hotels (around €50-100 per night). My grandpa can’t walk for long distances and isn’t very fast, so are taxis easy to use, or are there any accessible places that would be good for him to visit?

I also heard that WhatsApp isn’t available in China. Should we install WeChat to stay in touch while we’re there?

Thanks in advance for any advice!