I'm fine with replacing 'have to be' by 'must be'. Why do you prefer 'must'?
I'm not sure about 'these are' though. I think in Afrikaans, 'daar is' is generally being used for the Dutch 'er is' or 'er zijn' -> there is, there are. Or am I mistaken?
See for example this text about Afrikaans
http://www.let.uu.nl/nederlands/nlren/literatuurgeschiedenisZuidAfrika/begin.html
For me "must" and "have to" have the same function here and are interchangeable.
As for "these" or "there", in my humble opinion, if it was "these" the phrase would need to say:
"these are the precautions that have to be followed", since I find that the absence of article in case of the use of "these" makes the phrase extremely vernacular and informal.
I would stick with 'there' I think, unless AspieBrain can convince me I misunderstood the Afrikaans 'daar' (which is of course entirely possible!)
I've changed 'have to' to 'must' - I don't mind so whatever makes others (AspieBrain) happy