Can pages compete with each other? Inbound links & domain authority

[jpf566]

Heyy, I'm having some pretty big SEO issues.

We have had some drops in our ranking. We're 5th page or worse depending on location for a few of our keywords that we used to rank well for. There are all sorts of random non relevant sites outranking us for the term "stickley" and "stickley furniture"

One thing I noticed is that we are ranking for a different page for each keyphrase. Our home page is ranking for "Stickley" and our stickley page is ranking for "Stickley Furniture" Is this normal? I guess Google is just picking what it see's as what's more relevant. Is it possible that these two pages are "competing?" Do similar phrases linking to different pages cause pages to "fight" or unevenly disperse link juice?
I'm having trouble knowing which page I should send inbound links to since Google seems to be linking similar keywords to different pages. How much should I stress about which pages I receive links on? Is it true that any inbound link to a site site will help increase its overall domain authority and overall SEO?

What should I be focusing on? I've added 301 redirects for non WWW as well as tried to make the pages well optimized for SEO. Should I just add more related content to the pages?

I know backlinks are important but I'm having a really hard time figuring out how to get links that aren't just spammy forum post footers or junk directory submissions.

The thing that bothers me is we were ranking well and then suddenly are wayyyy back. We have never done any black hat SEO of any sort. I feel a bit stuck and confused at the moment

Thanks in advance for any help!
-Amy