According to www.meertens.knaw.nl Van Himst and its variants (which are many, but one of them being Van Heemst) are toponyms deriving from the placename Heemst. But at this point it is unknown which town or village is meant. What i personally do know is that the component heem in placenames had the meaning of 'dwelling-place', as in placenames like Heemstede, Arnhem and Bentheim. But in this case there is the Dutch word heemst , meaning 'marsh mallow', which is a plant, i think it's the plant of which they extract the sugar that they use to make marshmallows. As there is also the Dutch surname Van der Heemst (the der part suggest that the next word is a noun and not a placename; compare: Van der Berg ('of the mountain'), Van der Kruis ('of the cross'), this is more likely to be related to an area where this plant grew and where the ancestor is from.
Tindemans: I can't find many info on this one, but i tried Google.com and found also Tinnemans, which would mean in English 'tinman' and thus would be a name deriving from a profession related to tin. This is probably only the element tin and not tin cans, which in English through time was shortened to tin . This in Dutch is blik nowadays, but maybe tin used to have this meaning in Dutch too. But there is also the Dutch word tinne , which is from Middle Dutch tind (and there is the 'd' again). This word means 'crenel', which is the hole in a castle (or its tower) through which people and/or canons shot at enemies. In this sence the surname Tindemans could also derive from a profession, but this time someone from a castle, maybe a person shooting through these crenels. The second one in my opinion is the most logical, because the Dutch (and English) word tin is from the Old French word tain or étain , which would leave us the question where the 'd' in Tindemans is from. However, the second option does give this answer because it used to be in the root ( tind ).