okay, it was the legal terminology that confused me. Thank you.
This one I am really struggling with (i don't think the lack of punctuation helps)
et ego dictus Thomas et heredes mei dictam terram cum pertinenciis dicto Willelmo et heredibus suis contra omnes gentes warantizabimus et defendemus imperpetuum
'and I said Thomas and my heirs will in appurtenance my land from William and his heire's will warrant and defend against all the nations'.
I am unsure if william and his hieres (assuming that is correct is in the dat or abl)?