That's quite a sweeping and juvenile generalisation about people who have a different political approach and mindset to you. It doesn't sound like you are genuinely interested in understanding various political outlooks, and maybe you believe there is only 'one true' political view which conveniently happens to be yours?
The FPTP system has an unfortunate downside that it effectively turns into a two party state. So the Labour party will attract all kinds of left wing people - from fairly mainstream left leaning people to far left nutjobs and cranks. Similarly, the Conservative party will attract all kinds of right wing people - from fairly mainstream right leaning people to far right nutjobs and cranks.
Both parties tend do well when they appeal to the broader and more centrist views of the general population, rather than niche, radical ideological purists. But of course when you try to be all things to all people, this can end up leaving everyone frustrated. The Conservative party doesn't seem to be genuinely conservative these days.
Left wing approaches tend to favour bigger government, more public spending, while right wing approaches tend to favour smaller government and less public spending with more private investment and a belief that the market can solve issues better than the government.
Both left wing and right wing people can care about similar issues, but have different values and approaches to how they think socioeconomic problems can be solved.
For example, in terms of lifting people out of poverty, left wing approach tends to be focused on government giving money with additional bureaucracy to handle the administrative system required to deal with all the payments.
Whereas the right wing approach might be to reduce government bureaucracy and loosen up business rules and trading restrictions. This can make it easier for people to set up new businesses and can encourage small and large companies to expand and create more jobs - and they will hire more people, which means the economy will grow and people will be gainfully employed and therefore able to earn their way out if poverty.
There are pros and cons to each kind of approach. And there's plenty of literature and analysis to read if you are interested.
But you're better off talking to your relatives and trying to understand their concerns and why they feel they need to vote Conservative. Everyone tends to vote for what they feel is the least worse option. That's the downside of the two party system.
Maybe they have some valid justifications, maybe they have some concerns but are under the misguided impression certain policies will work, but there's no evidence to indicate such issues will be resolved etc. Rather than being preachy or making sweeping judgements about them or the policies they vote for - you might have to learn that you don't always have to agree on everything in a family.