My eldest crawled at 8mths, walked at 13mths, my second crawled at 4.5mths, then started walking upright, but on her knees (you kwim? like when you shuffle along on your knees) until 9mths when she started walking properly. My third crawled at 6mths, walked at 9mths and they all have roughly the same level of coordination - they aren't outstanding, but are at age appropriate stages although our eldest is extremely long sighted so that affected his distance judgement sometimes when throwing at catching balls, but thats not an issue now. My fourth has started crawling at 6mths too. They did have excellent manual dexterity skills though and could screw bottle tops on at 10mths old etc. On the other hand, my Nephew (DHs brothers child) is THE most uncoordinated child I have ever seen - this kid will be walking on a level surface and just trip over. BUT he has had about 6 severe ear infections and he is only 2yo. Did your BIL have a lot of ear infections as a child? Sometimes when you have problems with your inner ear, it can affect your equilibrium (your state of balance) and make you very unsteady on your feet etc and I suppose it would be reasonable to expect this to follow on to other aspects of coordination.