Best places to travel with old folks to Taiwan

My travel group will include some old folks. What are the best/ most recommended places to travel for old folks without involving too much walking or transportation transfer as some of the old folk gets travel sickness? And among Ali Mountain, Mt Yangming, Jade Mountain and Sun Moon Lake, which are the most suitable for old folks? Period of travel would probably be around 8 to 10 days and we plan to stay in Taipei and maybe in another county (Kaoshiung perhaps) that is near to the attractions and old folks friendly, thus any recommendations . And would April be the best reasonable time? Thanks in advance for your advice.