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Both signals have frequencies between 2Hz and 5Hz.
The frequencies overlap so cannot be separated with filters.
Now you say the frequencies do not overlap.
If you use a 4th order Butterworth lowpass filter for -3dB down at 5Hz, and a 4th order Butterworth highpass filter for -3dB at 10Hz, then the lowpass output at 10Hz is -24dB and the highpass output at 5Hz is also -24dB. Only 24dB is not much separation.
All harmonics of the low frequencies will appear in the output of the highpass filter.