The endsleigh policy won't be as good…end off.
Try and pursuade your folks to switch to M&S on their next renewal. Offer to pay say £100 towards it…that should help their decision.
Seriously, M&S are top for bikes. Greenbee has very similar cover but tends to be more expensive.
Edit: Actually you really do need to get them to switch policys. Being dual insured is a bad thing, as the insurance companies may argue over who is liable. Imagine your house got burgled, and you tried to claim for the bikes from M&S, and your parents claim for the electrical goods from their insurance company. Not advisable…