Deciding to buy just presents for kids while expecting them from adults with no children in the household (aunts/uncles/grandparents) is cheeky. Its about reciporically showing you care... and children should learn to give not just recieve.
If someone wants to spends £10k on 150 presents for their toddler, its their choice. Same if you spend £5 on one present.
Santa IS definitely real. Not as a person buying presents, but as the embodiment of the acts of kindness that happen around Christmas time. (For example the local Giving tree clears out of tags as soon as they put them up... buying presents for people/animals from various charities. Homeless, elderly, children, pets shelter... they all go straight away. )
Christmas day is just as fun with small groups. You don't need 20 people in a small house. In fact it can be more enjoyable