Are the houses that your boyfriend's mum finds (and books viewings for) houses that are appropriate? Or are they in the wrong location, or the wrong price, etc.? If she not locating appropriate houses, then let he know what sort of thing you're looking for. If she finds the perfect house, would you dismiss it just because she found it, rather than you? If she's finding "good" houses, I don't understand why you wouldn't welcome the help.
Also when you say, "I would prefer it to be my parents to help out if needed", are you still talking about searching for the house or are you talking about them helping in some other way (e.g. financially)?
Is your boyfriend "allowed" to help with the search too, given that he will "save up to match my deposit so we’ll eventually be 50/50 on the house". If he's allowed to help as an equal participant, they why would his parents not be treated equally with your parents?