Welcome to Diyaudio.
You can connect two 4ohm speakers to two separate channels, but do not connect two 4 ohm speakers in parallel to one channel.
The reason is that when two 4 ohm speakers are connected in parallel, the impedance will equal 2 ohms, which the amplifier cannot handle safely.
You can connect two 4ohm speakers to two separate channels, but do not connect two 4 ohm speakers in parallel to one channel.
The reason is that when two 4 ohm speakers are connected in parallel, the impedance will equal 2 ohms, which the amplifier cannot handle safely.

Two 4ohms speakers connect in series the impedance will equal 8 ohms and should be safe for the amplifier to drive.
Welcome!my amplifier
What make/model are the amp and the speakers? And radio?
Yes you can wire in series but it is not best for the sound. You can wire in parallel which will be fine UNLESS you crank it way up, then the amp will get too hot. Seems like you need another or different amp...