Group schemes do not solve for long term personal finance. So a generic view is that avoid group schemes as much as possible. Read this article: Should you buy group insurance sold by banks or apps? Group Insurance Vs Retail Insurance (beshak.org) 

Group policies should be bought 

• For the short term, when you want to cover some immediate illness/treatment
• as a last resort, when you aren’t getting through any other long term health insurance product (due to age or medical history)

You must continue your personal topup. Personal plans are in your control, and not dependent on the group plan (which can get withdrawn/curtailed based on the claims experience, viability of the product). Premium for personal plans cannot be hiked, or the product cannot be withdrawn based on individual claims. 

Yes, you can take multiple topups - they will work - one over the other. The only fine print is you may not be able to get cashless for all the policies for one hospitalization. 

Yes, you can. But you must not. Group is a short term, one year policy that an insurer can withdraw, change terms, including premium every year based on the profitability of the product. Personal Insurance is a long term solution that is in your control, and has much better regulations to cover you for your old age than a group plan. 

All of these can be claimed in one hospitalization. Albeit, if the hospitalization is of a short duration, then you may have to claim the topup as a reimbursement claim. 

How to claim in multiple policies: 2 Different Health Insurances Policies from Different Companies - Beshak

No, you don’t have to. There is no requirement in the policy or the regulations.