Battery powered amp

Blackstar FLY3. I personally prefer the guitar version as I find the delay on that one more useful than the compressor on the bass version, but they use the same boxes and speakers for both versions. I have and use both for campfire talks in my ranger job because the acoustic guitar around the campfire has been done plenty. Spring for the extension speaker and power supply, and you’ll have a nice bedroom or headphone setup. I use mine primarily for playback through my computer. You can even plug in and play along

Roland Cubes also seem pretty good and have more features, but they’re too big to wear in a fanny pack like I do with my FLY3, haha.

 

Depending on how quiet you play together (you didn’t mention whether the two guitarists have battery powered amps, or are playing unplugged), there are choices. Here are two links to reviews of several amps.
Battery Powered Bass Guitar Combo Amp |.

Best Lightweight, Battery-Powered Portable Bass Amps - Range of Sounds

 

I have both the Blackstar Fly3 Bass Duo and the Phil Jones Double Four. The PJD4 is a high end excellent amp, about $550 US with the battery, the Fly3 Duo is about $130 US and I've used it in a park with about 10 unamplified acoustic players, works well, but if you're willing to spend the money, nothing is better than the PJD4.

 

Great setup and sounds great.

 

This isn't strictly a bass amp but after looking at all other battery-powered amps, this looks like an affordable option. 40w, multiple channels, and rechargeable. Some guy ran his drum machine through it so it must be able to handle some boom. The features are insane for the money.
https://www.amazon.com/Acoustic-Amp...07S9D9JYN/ref=cm_cr_arp_d_product_top?ie=UTF8