Maybe You're right... I'm looking for a cheap solution for receiving on a fixed frequency (or tuning within very small range) on VHF
Can really use two convertions by one si5351 chip?
For example, IF1 80 MHz - filtering - and already low frequency
yes, you can do 3 conversions by using single si5351 chip. It has 3 channels. But it has only two PLL, so if you want to use all 3 channels it requires to share one PLL for 2 channels, as result third channel frequency setting is a little bit limited, because you can configure only divider for it since PLL multiplier needs to be set the same for two channels.
you can buy si5351 module on aliexpress (magenta color) they are very cheap now, but these cheap Chinese modules uses cheap oscillator with high temperature dependency and high initial frequency error. I have also Adafruit version of si5351 module (blue color), it has better TCXO which has less temperature dependency and less initial frequency error.
Also notice, that there is some parasitic crosstalk between channels, so if you want to get the best spurious performance it's better to use separate si5351 for each carrier.
I'm using shortwave transceiver, it uses two channels of single si5351for superheterodyne and it works good enough.
I tested the same transceiver with frequency synthesizer on
AD9952 (400 MSPS 14-Bit DDS) and can approve that si5351 version has much more clean output with much less spurs.