Is it risky to delay the completion date when selling our home?

Our sellers want the whole chain to exchange contracts in March but to complete in JulyQ I have an unusual situation I’m hoping you can help me with. We are in a relatively short property chain – we are selling our current house to first-time buyers, and we are buying a house from people whose onward purchase is the end of the chain.They want to do a substantial amount of work to the property they are buying and have suggested that the whole chain exchanges contracts in March but wit