"Those who eat from the earnings of their daughters and sisters will receive heavy punishment from the Angels of Death.."

Rehatnama Bhai Nand Laal Jee

does this mean i should never have eaten food when visiting my sister?

The rehit is refering to those who live off the earnings of their daughters and sister.

There is nothing wrong with eating a meal at your sisters or daughters house.

If their house is Gurmukh, how and why would you refuse - they are sangat?

lol I don't think this refers to going over for a meal made for you out of love :)
Its not about eating specifically, its about people who leech off their daughters and sisters, i.e. not working themselves and being dependent on them.

bhull chukk maaf, any gursikhs please correct anything i said wrong.

Agreed. We are not supposed to be leechers/living off the earnings of others BUT self earning..Honest Kirtees earning by our two hands, wand chhaking that earnings. GURU NANAK JI SAHIB started that pirt...Honest labour is Hallmark of each and every SIKH.

a Sikh is never a "free loader"....on his parents..or siblings...or friends...or anyone else for that matter (Arguably if a person gets the habit of freeloading/living off the earnings of his isters/mother..he MAY surely graduate to living off the erarnings of others and that would be PIMPING and it is punishable by Law in many countries ).

A Sikh is also never a Beggar. That is also a type of freeloading...and demeaning.

This habit of not taking a sip of water even at the daughter's house is an old time part of Punjabi/Indian culture - a Gursikh can certainly eat and drink at his sisters House...Just Follow Sahib Sri GURU NANAK JI SAHIB's example at the house of Bebe Nanki ji. Bebe Nnaki ji would always "invite" Guru Ji through the strings of her heart...and Guru Ji would always turn up to have his meal. In fact it was Bebe nanaki Ji that took away Guru Ji from Talwandi to Sultanpur.
Sikhi-Gurmatt is LOGICAL...not illogical set of myths..

JSGyani

a lo of stuff out there, rehitnamai,even some sakhees are not true
read guru granth sahib, and thenull kno for ureself wats true and wats false
make sure u dont close ure mind off to anything, cuz if we do then thas out of hankaar
let ure mind be open, read guru granth sahib je in that sence, with a clear mind
and ull see a line like this is jus wrong, as many things are out there