Which is it: "low income housing" or "affordable and market rate housing for seniors"? They're not the same thing.
Nadine makes a valid point about the style and quality of houses fitting in with the neighborhood. That's important. However . . .
Your neighbors are also concerned about the style and quality of the residents fitting in, as well. (Lot of posters here understandably are nervous/reluctant to suggest that.) I'm absolutely not saying that the residents of a low income (or even affordable income) housing would be any different--except economically--from the residents already there. But there may be a concern among some current residents that along with the lower incomes may come other problems--drugs, crime, etc. That'd be less of a likelihood with senior housing, of course, but there's still a concern that the new residents may be different.
Again, recognize the validity of Nadine's point. But go beyond that. I'd suggest reaching out to the surrounding community and making the argument that the new residents will be a benefit to the community, not a detriment. Contact a local college that has a journalism/public relations track and talk to an instructor there. Try to get some free advice. The first thing I thought of (I've got a background in journalism and PR) is an outreach program. Profile individuals who would be moving in, or at least typical seniors who are living in similar nearby facilities. It might be an elderly man who served with distinction in Korea, returned home, started a business (or worked in a business), and then retired. An older woman who was married for 40 years until her husband passed away, and whose kids have become teachers, firemen, etc. In other words, humanize the residents. It's easier for neighbors to be concerned about "low income housing." It's far more difficult for them to hate or fear someone with an engaging, uplifting story.
Hope that helps.