Hi newmum and congratulations on your new Lo
Are you feeling under pressure from your DH and HV to get Lo sleeping through? I'm sorry but your HV is wrong. Sleeping through is only classed as 5 hours so if your Lo is going to sleep at midnight, then waking for a feed at 5am, they are sleeping through. Is there a particular problem with her sleeping that your DH is worried about? If you give us more details we may be able to help
I think its also important to remember that there is a huge variation in what is normal for a baby and sleep. While some will indeed be sleeping through at 8 weeks, they are a minority. What your baby needs right now is knowing you are there for her and milk whether that's BM or formula
Have you come across the isis website yet? Its a great resource for parents and HCPs and perhaps you should tell your HV about it too!
There is some information on ISIS regarding sleeping through the night which you and your DH might find helpful
Personally I wouldn't put cereals in a bottle. Firstly, its a serious choking hazard and you need to make your DH and both set of parents aware of this, just in case anyone gets the bright idea of trying it while you're not around.
There is also some evidence that introducing foods such as cereals, and don't forget that rusks are full of sugar too, can interfere with your babies insulin levels and can leave her prone to developing diabetes later on. The cereal will also take up tummy space that is needed for her milk. It will stop her being able to regulate her own calorie intake which could lead to problems with her growth development and could lead to obesity later. Also, as it will interfere with her insulin and her ability to regulate her calorie intake, it could lead to more night wakings, not less.
Before you consider giving her anything other than BM or formula have a read of this. Its a really good article and includes things like the signs of readiness. Personally I wouldn't give anything other than the formula until she meets those signs.
All your baby needs until they are six months is BM or formula. While some people do wean before 6 months there is evidence that weaning before 17 weeks can cause harm. Whether you put food in bottles or on a spoon, it is weaning. The kind of harm that it can cause are things like IBS, Celiac disease and increased risk of allergies. Your parents may well have done this but you need to toughen up and ignore their "helpful advice".
Since they were parents there has been 20-30 years of research and thankfully we now have evidence on why things like this should just not be done.
My Aunty was always trying to get me to wean my DC early. She weaned hers at a similar age to your dd. My Aunty just does not seem to be able to associate the early weaning with the fact that all of her children have digestive problems and her youngest has asthma, had a heart attack in his 20s and had to retire at 50 due to ill health.
If you do want some help on improving her sleep have a read of 31 ways to get your baby to sleep and stay asleep. If you want a book to read try Baby Calming by Caroline Deacon. Your library might have a copy. I'd also get your DH to read them too
Sorry for the huge post but I didn't want to say "no, don't do it" without explaining why it might not be the best idea and also giving you some ammo some good information so that you can decide for yourself.