First time buyer options

Yellowstone2

I'm hoping to buy a house or flat within the next year and starting to do some research. 

I have saved about £25k by working full time and living at home for 3 years since leaving Uni, and I also have a 'help to buy' ISA with about £5k, so hopefully I will have a decent deposit.

My parents have also offered to 'lend' me some of their savings. They suggested cashing in £20k of their premium bonds so that I would have a smaller mortgage, which is fantastic and I do know how lucky I am, but I'm not quite sure how that would work yet. They just say they I could give them the money back when I eventually sell the house, but I'm thinking it's not as easy/straightforward as that.

Would I actually be able to use my 'help to buy' ISA if my parents were involved with the purchase? (As they are homeowners)

As a rough guide, should I be looking at a mortgage of no more than 3 times my income? (I don't want to overstretch myself, especially as I would be buying on my own, not with a partner) 

If I bought a 2 bedroom property and a friend moved in at some point and paid something towards the utilities and food etc, would I have to inform the bank? (I'm sure I remember something about certain types of mortgage restrictions if it involves other tenants in the property)

If anyone can point me in the direction I need to go with the above questions that would be great. I know I need to do my own research, I just need a few pointers. It's just exciting to think that I might be able to buy my own place. (Something I never thought I would be able to do after Uni, with the weight of what I owe to student finance, and not getting a job straight away)

ACG

Parents can help with a deposit if you use your HTB ISA yes. However most lenders will not accept a loan. Parents would likely need to gift you the money. If you subsequently decide to pay them back, thats your choice but if it is a requirement, it probably wont be of any help. 

You can lend up to 4.5x income, but if you want to lend less that is understandable and completely optional. There is no point having a nice big house and no money to anything. 

You would not need to tell the bank no. There is a scheme called "rent a room scheme"- have a read up on that. 

Speak to a mortgage broker. They will be able to help with a lot of your questions.