For "family" there is familia, but most of the time it didn't actually mean exactly what we mean today by "family", but the whole household including all slaves etc, even if it sometimes meant "family" as well. Now I think it might not be the best word to use here; as you're speaking specifically of your father, mother and sister, I think this would have been expressed more naturally in Latin by proximi, that is literally "the closest ones".
My family, my strength: Proximi mei, mea fortitudo Familia mea, mea fortitudo - or robur meum, which could be "strength" or "source of strength".
My strength comes from my family: Fortitudo mea e(x) proximis meis venit Fortitudo mea e(x) familia mea venit
Or fortitudo mihi e(x) proximis meis/familia mea venit, which would be literally "strength comes to me from my family".
Now I'm not completely sure that "strength comes from..." is very natural Latin - but I may be wrong, you can wait for what others say. Now if you choose the version with robur for the first phrase, the idea may be somewhat included in it, as it can mean "source of strength", so where it comes from...
My family, my foundation: Proximi mei, meum fundamentum Familia mea, meum fundamentum
Thank you so much for your answer! I think i will choose the word familia because it looks better than proximi. I was thinking in some small phrase, like 3 or 4 words, because the tattoo will be in my arm.. something like "Fortituto per familiam". which means strength throught family. Is that correct? I was thinking in change "throught" to "from", or "coming", so it will be like "strength from family" or "strenght coming from family". could you translate please?
Because the preposition per requires the word that follows it to be in a different case (a different grammatical form). Words decline in Latin, they have different endings depending on the function they have in a sentence.