If I proceed with the brotherhood missions does it cancel out and others?

I believe its only the main story missions that lead to the end of the other factions, I'm currently doing missions for several factions including the Brotherhood and haven't reached the cut off point yet when I will have to make any permanent decisions......the police station missions are repeating missions (clear out and recover tech), as is the escorting the Scribe mission and there was also a BOS mission about missing rations that I completed.

Its hard to get into details and stay in non-spoiler territory.

That's the perfect non-spoiling answer thanks

Oh and just in case you miss them there are couple of cap quests with BOS as well, one is for blood samples and the other is for technical documents both of which your will find a lot as you explore the world so remember to talk to every named NPC on the airship.

You will make enemies no matter who you side with the game will warn you when such a decision has to be made best advice I can give is don't run through the main quest line to fast explore the factions some can offer you some nice stuff and you can do quests for ALL of them up to a point

The game will tell you in a warning box 'This action will make you permanent enemies with blah blah blah' when you reach that point.

I don't want to spoil anything, but don't worry about accidentally going too far, as long as you don't do any missions that clearly state that you are killing another faction, you will still be safe. Though, there is a point when you talk to Kells and it gives you no options to say no... but I just reloaded my save right before talking to him.

With the Brotherhood that is, there is a certain Minutemen mission that if you take will make you forfeit the Brotherhood of Steel ending. This only happens after already forfeiting the other two factions though.

Yeah, you'll know when you're hitting the point of no-return. I don't advise going past it until you're ready to move on from major side content, because stuff happens and certain avenues will be closed off to you.