Obviously, the bots sort of understood what it meant when Chief said Woodrow was his brother, but the bots had a differemt viewsite upon this.
For Cybertronians, siblings aren't actually related to one another. Their genetics are completely different to each other, which also argues why some bots have said that they technically don't have siblings. Although two bots may have the same Sire and Carrier, their codes are completely different from one another. The only codes they will match with are their creators, not their siblings.
Now this also brought up somehing else, because apparently, Boulder did think that Heatwave and Blades were these 'siblings'. Much questions were brought into this with the bots and their private discussions, to which Blades and Heatwave had to physically explain that they were never related to begin with.
That explaining actually took way longer than it needed, as Boulder still didn't seem to understand how it was (yet again, some information was left out). It wasn't until Blades showed an actual picture of his creators, which looked nothing like Heatwave but did have much resemblance to Blades.
Heatwave then asked what had happened to the other Mech in the photo since he never met him, but when Blades responded with 'I don't know', they knew that the conversation was done.