Go to www.nationallienlaw.com
and buy a "notice of intent to file lien" $15-20, it'll give you a PDF that you can use unlimited times for whatever accounts/addresses you need to. Then if after 2 weeks they haven't responded for payment, buy the lien (another 15-20 bucks) and you can use it unlimited times.
This way, you're only out of pocket $40 or so and you get to use the form for the rest of your business life. It's way cheaper than $300 per lien x 8 homeowners.
With the "intent to file lien", I would send a brief cover letter to each homeowner stating to the effect, "we have tried unsuccessfully to collect, bla blabla. Filing a lien is the last thing our company wants to do, so we ask you to please have your management company contact us with payment arrangements since we have not been able to get any response for them."
You will want to send a copy of your original invoice, a copy of the notice, and the letter to homeowner
Lastly, if the payment date comes and no arrangements have been made, then send a copy of the lien to homeowner. You will need to go to your county clerk office to file the lien as well.
hope this helps.