High protein pulses have more than other veggies but less than meat, especially processed meat.

As with many things nutrition related, there’s often not a direct line between the contents of a food and the resulting concentration in our blood stream. Foods with cholesterol do not directly cause high cholesterol in the blood it’s the same with purines and uric acid.

Speaking as someone who has/had gout, my weight and how much sugar I eat is really the only thing that correlates with my uric acid results.

I’ve eaten 70g of lentils and 170g of cauliflower for breakfast everyday, 100g of spinach for lunch, and often asparagus and/or broccoli for dinner. Apparently these are veggies that are high in purines and “should” result in a raised uric acid level, but I’ve actually seen my levels reduced. A study can be found here.

If your family is concerned about uric acid (which is valid as high levels can lead to adverse health outcomes), I’d recommend getting a blood test and seeing what your levels are actually at and what foods actually drive that number in you.

I believe the sole issue with uric acid levels is that at excessive levels uric acid can crystallize in the joints causing arthritis-like pain known as gout. Uric acid is acquired by consuming foods with purines, which we metabolize into uric acid. (So 'which foods are high/low in uric acids' is a bit of a simplification and doesn't produce great search results).

Here is one site that lists amounts of purine and uric acid in various foods. Values for lentils seem pretty similar to meat products: https://dr-barbara-hendel.com/en/nutrition/tables/purine-content-table

However, I wouldn't advise that you focus on refuting your family's claims that lentils have so much uric acid that you should stop eating them. You may want to mention that lentils have comparable uric acid to meat. But I don't think your family is arguing in good faith. They may be cherry-picking anti-vegan arguments with little information or true concern about reality and are essentially just placing a huge burden of proof or justification on you for your diet (while they face no scrutiny).

So don't go after the hypothetical omni 'what if about nutritional unsoundness'. Say I'm glad you're concerned about my nutritional well-being. If you think I might be at risk for gout, let's go get me some bloodwork. And if my uric acid levels aren't anything to worry about, then you don't need to worry yourself any longer about my lentil consumption

https://nutritionfacts.org/?s=uric%20acid