Depending on their knees, legs, back....a kitchen height bar stool might be the easiest for older people. Table height chairs and lower can be harder to get up and down and put more strain on knees. I would get counterheight stool that are padded (square not round seats) with a back on them. Unless they are in a wheelchair? Then, yes you should do a table height. I've always found two tier island with chairs awkward looking....unless you do a T -shape or an extended table design. I did a minimalist/modern kitchen a few years ago for people that entertained a lot...they wanted both height seating on their island as they were getting rid of the kitchen table. See pic below.

Extended Table Island shortly after install

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I've never really liked this concept. Looks pretty...but I wouldn't want to sit that low.

Here are some ideas - but def not recommending any of them, I usually think that a traditional island workspace and then a separate table seems to work best for everyone (I think sitting at eye level with the chopping/washing would not be great)

I have to agree with others that this concept is not the best for those sitting at the island.

I am 76 yrs old and still like to sit at the counter on a stool . I do not love bar height stools but counter ones are great for comfort. I do agree this is not a prctical or nice looking plan. BTW n island you cannot reach all the way across is not a good idea either .

If you have the space, what would be best for senior citizens in your home is to have an island that is one level at "counter height" which is 36" from the floor including the counter. Use that as an island, not for seating, but for food prep. And separately have a regular round table for them to sit at. My mom could not have sat on a stool at a counter regardless of the counter's configuration. Nor did she want to lean her arms - which were thin-skinned and often cold - on a stone or Quartz counter. She also would not have wanted to twist her neck or shift her seat to talk to a person sitting next to her at an island counter. It was much more comfortable for her to sit in a chair at a round wood table and have tea and meals there with her children/grandchildren.

I only have 2 stools at my "counter height" island and we rarely sit there as we have a 60" round table a few feet away in the kitchen eat-in area. Just beyond the round table I also have 2 comfortable chairs facing the kitchen, making a small sitting area. This is where my Dad sits with his iPad when my Mom and I are working in the kitchen.

Even when my mom had just had her hip replacement surgery, she had no problem sitting at my counter-height bar. The key: my barstools swivel ... she could just "back into one", then turn around to face the bar.

A separate table is much more family friendly than gathering around the dirty dishes and sink full of cutting boards.

Absolutely. 2-3 barstools are plenty ... but have a nice table nearby for meals.

wow a lot of responses in a short amount of time. thanks for all the advice so far. I agree having a separate table would be best but we just cant find the room for it in a floor plan as my mom would like to have a formal dining table and a kitchen table in an open space. She is a bit on the short side and on the heavy side as well so jumping up to counter height stool might be a little rough for her. The sink will not be on the island as the cooktop will be there so the main island would be for cooking and food prep with the sink against the wall. and the table part would be for all to eat at not separate eating areas. loving the ideas though and again thanks. will look into more counter height seating options maybe can find something that would work. Just don't want any bar height things.

There will be others chiming in, but a cooktop on an island usually isn't the safest/best place for a cooking apparatus plus the necessary overhead vent looks intrusive and ugly dropping down in the middle of the kitchen. Downdraft ventilation isn't the answer unless cooking is minimal in the household.

If you post a hand-drawn floor plan (graph paper with measurements), then no doubt the pros can figure out how to incorporate a kitchen table if there's space for an 11' long island. Older folks are safer on chairs vs stools of any kind or height (swivel seats can shift when sitting down precipitating a fall too).

I know that islands are preferred by most. I am a healthy agile senior and still prefer to sit at a table for meals. Though we have room for an island, I have a good sized table instead. I cannot be relaxed and as conversational at counter height. My exception is when I am at daughter's house sitting at counter munching, watching her prep.