I wouldn't under any circumstance agree to take out the stipulation regarding selling your own house. QUOTE]
Sellers of new property are not going to contract themselves into a chain. Selling second hand most sellers prefer non chain purchasers. Builders dont even go there.
If you are very concerned (and I hope you are not) that you will not be able to (1) sell your house and (2) get somewhere near what you expect to get or need to get to be able toaffors the new house, then I think the best thing to do is to pull out, as at this stage no binding contract exixts.
Good luck with what ever you decide.