The RSL Outsider II are rated at 8 ohms, with 6.5" bass driver with response down to 50hz. That's about the best you can expect from a speaker like this, and I suspect few can equal it for performance.
Since they are 8 ohms, with the right amp you could drive Four Speakers. If you have Speaker-A & Speaker-B switches on the amp, most do, then you can have Fence Speakers only, On-house speakers only, or both simply by switching the speakers in an out.
That would be about $400 for Four Speakers. Then we need to consider the Amp to Drive them. How much can you spend on that?
I would suggest Bluetooth, that way you can Stream from a Smart Device (phone, pad, tablet, computer) to the amp. Bluetooth is not the absolute best for Music listening, but for background music at an outdoor venue, it is going to be fine. But a dedicated Bluetooth Adapter runs in the range of $25 up to about $80 for low-latency lo- range devices.
Though of course there are hundred to choose from.
So, that leaves us with the Amp. How much are you willing to spend on that?
Just one of many possibilities -
Yamaha RN-303 Network Receiver, 100w/ch, Network Streaming, Bluetooth, DAC - $299 -
With Network Streaming, while you would use your Smart Device to browse, select, and control the music, it would actually Stream through your Home Network.
If you want to go for a more minimal amp, then consider -
Yamaha RS202, AM/FM, 100w/ch, Bluetooth, - $130 -
Likely the built in Bluetooth is going to be limited to about 30ft line of sight.
I think the Linked Avantree are about 100ft line of sight.
Just a few thoughts.